13.2 Types of Infectious Disease Outbreaks

Influenza

Influenza viruses cause influenza (flu) A and B, which result in a respiratory infection affecting the nose, throat, and lungs, causing mild to severe illness and sometimes death. Influenza viruses are categorized as follows:

• Influenza A viruses cause the most severe and widespread disease, undergoing minor mutations (antigenic drift) each year and periodically undergoing a major mutation (antigenic shift), which results in a flu pandemic.
• Influenza B virus often causes milder disease outbreaks, mutating gradually via antigenic drift but not undergoing antigenic shift.

Flu often occurs in the winter months but may be found year-round with testing. Each year, approximately 8 percent of the U.S. population becomes ill from flu viruses, with children twice as likely as adults over the age of 65 to develop symptomatic flu illness (CDC, 2022x). The seasonal incidence of flu changes based on the severity of the flu season. Seasonal flu is very different from pandemic flu. Seasonal flu viruses often undergo antigenic drift, necessitating an annual flu vaccine that is updated yearly to reflect current circulating influenza strains. In contrast, a major mutation resulting in a new influenza strain (antigenic shift), such as those that have occurred four times in the last 100 years, is often responsible for pandemic flu (CDC, 2022t). Hosts are more susceptible to these new disease strains as they often have little to no immunity against them (CDC, 2022t).

Flu is easily transmitted by droplets of infected material. When infected individuals talk, sneeze, or cough, infectious droplets can land in the mouths or noses of individuals nearby, spreading the disease. The flu can also be spread through indirect contact transmission (CDC, 2022x). Infected individuals are most contagious during the first three to four days of illness, but some are contagious beginning one day prior to symptom onset and up to seven days after becoming ill. Anyone can get the flu, and serious problems may occur at any age. Older adults, children under five, pregnant persons, and individuals with chronic conditions such as asthma, diabetes, and heart disease are at higher risk for developing flu-related complications. Flu symptoms include fever, chills, cough, sore throat, nasal congestion, body aches, headaches, fatigue, and sometimes vomiting and diarrhea (CDC, 2022x).

Pneumonia

Pneumonia is a lung infection that causes mild to severe illness in individuals of all ages. Risk factors are age (older than 65, younger than five years), co-occurring chronic medical conditions, and cigarette smoking. Viruses, bacteria, and fungi are agents that can cause pneumonia. In the United States, the most common causes of pneumonia include:

• Viral: Influenza, respiratory syncytial virus (RSV), and SARS-CoV-2
• Bacterial: Streptococcus pneumoniae (pneumococcus), Mycoplasma pneumoniae, and Chlamydophila pneumoniae
• Fungal: Coccidioidomycosis found in Southern California and the Southwest deserts, histoplasmosis mostly found in the Ohio and Mississippi River Valleys, and cryptococcus found in soil contaminated with bird droppings (American Lung Association [ALA], 2022)

Some types of pneumonia are contagious, spreading via droplet transmission similar to the flu. Individuals may also spread pneumonia through indirect contact transmission, and not everyone exposed to pneumonia will develop active disease (ALA, 2022). In 2021, over 40,000 individuals died from pneumonia in the United States. Many of these deaths could have been prevented or avoided with vaccines and appropriate treatments (CDC, 2022ab). Current vaccine options for bacteria and viruses that can cause pneumonia include COVID-19, Haemophilus influenzae type b (Hib), influenza, measles, pertussis, pneumococcal (PCV), and varicella. PCV protects against 13 or 15 (PCV-13 vs. PCV-15) of the most common serotypes and is a part of the routine infant vaccination schedule, while the 23-valent pneumococcal polysaccharide vaccine (PPSV23) is available for individuals in high-risk groups.

Pneumonia symptoms vary greatly but may include fever, chills, a productive cough, shortness of breath, rapid or shallow breathing, sharp or stabbing chest pain, chest pain worsening with deep breathing or coughing, loss of appetite, fatigue, nausea and vomiting, and confusion (ALA, 2022). In 2019, pneumonia killed 2.49 million individuals globally, one-third of whom were children under age 5 making it a leading cause of death in this population (Dadonaite & Roser, 2019). Within the United States, community-acquired pneumonia is a leading cause of hospitalization and results in significant mortality (Regunath & Oba, 2022).

Hepatitis

Hepatitis is inflammation of the liver and may result from a viral infection. In the United States, its most common viral forms are hepatitis A, B, and C (Table 13.2). Viral hepatitis infections affect millions of people globally, with hepatitis B and C resulting in chronic infections and liver cancer, disproportionately affecting lower-income countries. However, progress in treatment is being made globally. Hepatitis C is curable with a three-month course of medication taken once a day, and medications are available to slow the progression of hepatitis B and prevent liver damage (CDC, 2021e). Both hepatitis A and B can be prevented with safe, effective vaccines.

HIV and AIDS

Human immunodeficiency virus (HIV) is a virus that attacks the body’s immune system and, if untreated, progresses to acquired immunodeficiency syndrome (AIDS). No current cure or vaccine exists for HIV, but with proper treatment, it can be controlled and those affected can live long, healthy lives (CDC, 2022a). In the United States, an estimated 1.2 million individuals are infected with HIV, with almost 160,000 unaware of their HIV status (CDC, 2022s). Almost 40 percent of new HIV infections are transmitted by individuals who are unaware they have the virus. Risk factors include men having sex with men (MSM); individuals who have had anal or vaginal sex with an individual who is HIV+; having multiple sex partners; sharing needles, syringes, or other drug equipment; having a history of other STIs; and concomitant hepatitis or tuberculosis (TB) (CDC, 2022ah). The CDC recommends HIV testing for everyone between the ages of 13 and 64 at least once as part of routine health care and annual testing for individuals with risk factors (CDC, 2022r, 2022s).

HIV is transmitted through direct contact with infected blood and specific body fluids, most often through anal or vaginal sex or sharing needles, syringes, and other drug injection equipment. HIV transmission may also occur perinatally (pregnant person-to-child) during pregnancy, birth, or breastfeeding; however, this is now rare in the United States due to advances in HIV prevention and treatment (CDC, 2022a). The three stages of HIV infection include:

• Stage 1, acute HIV infection: Heavy HIV load in the blood, flu-like symptoms occurring 2–4 weeks after initial infection and lasting days or weeks. Individuals are very contagious during this time.
• Stage 2, chronic HIV infection (also called asymptomatic HIV infection or clinical latency): Individuals often have no symptoms but can transmit HIV. Individuals who adhere to prescribed HIV treatment may remain at this stage and never progress to stage 3. Without treatment, this stage may last a decade or longer, or may progress faster.
• Stage 3, AIDS: individuals have a high viral load and damaged immune systems resulting in opportunistic infections or other serious illnesses. Without HIV treatment, individuals with AIDS generally survive 3 years (CDC, 2022a).

The three available HIV tests are antibody tests, antigen/antibody tests, and nucleic acid tests (NAT). While these tests are accurate, no test can detect HIV immediately after infection. HIV antibodies may be undetectable to existing tests for up to 90 days after infection. Antigen/antibody tests can detect HIV 18–45 days after exposure, and NAT can detect HIV 10–33 days post exposure. NAT should be considered for people who have had a recent exposure or possible exposure with early HIV symptoms (CDC, 2022s).

Antiretroviral therapy (ART) is an effective HIV treatment that reduces viral loads to undetectable levels, keeping the individual healthy and potentially at stage 2 (CDC, 2023g). ART is recommended for all individuals with HIV, as soon as possible after diagnosis, regardless of CD4 cell count levels, since it is associated with a large reduction in morbidity and mortality compared with those who defer treatment (CDC, 2023g). When ART therapy is taken as prescribed and in conjunction with undetectable viral loads, multiple studies have demonstrated no risk of oral, anal, or vaginal sexual HIV transmission (CDC, 2023g). ART therapy coupled with undetectable viral loads also reduces the risk of transmission during pregnancy, labor, and delivery by 99 percent (CDC, 2023g). Many individuals achieve undetectable viral loads within 6 months of beginning ART (CDC, 2023g). Treatment as prevention (TasP) helps keep individuals who are HIV positive healthy and helps them to avoid transmitting HIV to others. Some individuals with HIV refer to TasP as undetectable = untransmittable, or U=U (CDC, 2023g).

Tuberculosis

TB is caused by a bacterium, Mycobacterium tuberculosis (MTB), which often attacks the lungs but can attack any part of the body. TB is spread via airborne transmission. When inhaled, TB bacteria can settle into the lungs, grow, and spread to other parts of the body (CDC, 2022u). Anyone can become infected, but certain populations, such as BIPOC individuals, individuals experiencing homelessness, and those living in congregate settings (correctional facilities, detention centers) are at higher risk of TB disease than the overall population (CDC, 2022p). Because TB infection does not always result in illness, it is often classified as latent TB infection (LTBI) vs. TB disease (Table 13.3). Individuals infected with MTB have an estimated 5 to 10 percent lifetime risk of becoming ill with TB disease. Some will have LTBI, others will clear the infection, and some, such as those with weakened immune systems (for example, individuals living with HIV, malnutrition, or diabetes) and individuals with alcohol use disorder and tobacco dependence, will have a higher risk of becoming ill with TB disease (WHO, 2022b). See Caring for Vulnerable Populations and Communities.

Globally in 2021, 1.6 million individuals died from TB; it remains the 13th leading cause of global death and the second leading infectious killer after COVID-19 (WHO, 2022b).

TB may be detected through testing (Table 13.4).

Despite its global presence, TB is curable and preventable (WHO, 2022b). Treatment takes anywhere from four to nine months and can be expensive without adequate health insurance, creating barriers for clients who are unable or unwilling to take medication for that duration or who cannot afford the cost of treatment (CDC, 2023m; Viney et al., 2019). Treatment for active TB disease often consists of multiple drugs, some with a high side effect profile. Inadequate treatment may result in treatment failure, ongoing transmission to others, and the development of drug resistance. Drug-resistant TB, which occurs when the bacteria become resistant to the antibiotics normally used to treat it, is a public health crisis. Drug resistance is more common in individuals who do not take their TB drugs regularly, in those who develop TB re-infection after being treated for TB in the past, and in individuals from areas of the world where drug-resistant TB is common (CDC, 2022i).

Noroviruses

The highly contagious norovirus is the leading cause of vomiting and diarrhea from acute gastroenteritis in the United States across all age groups (CDC, 2023l). Each year, there are between 19 million and 21 million cases, with over 100,000 hospitalizations and approximately 900 deaths; these cases occur more commonly between November and April (CDC, 2021c; CDC, 2023l). Older adults and children under 5 are most likely to have complications related to norovirus. By age 5, one in 110,000 children will die from norovirus and one in 160 will be hospitalized (CDC, 2023k). Though they are often referred to as a “stomach bug” or “stomach flu,” none are related to influenza viruses (CDC, 2023l).

Norovirus is transmitted via the fecal-oral route through contaminated hands, food, or water or by contact with contaminated surfaces. The most common symptoms include nausea, vomiting, diarrhea, and stomach pain that often resolves within 48 hours (CDC, 2023l).

Common settings for norovirus outbreaks include hospitals, long-term care facilities, restaurants, schools, childcare centers, colleges, and cruise ships. Foods commonly implicated are leafy green vegetables, fresh fruits, and shellfish (CDC, 2021c).

Non-typhoidal Salmonella

Salmonella bacteria are classified as “typhoidal” or “non-typhoidal.” Typhoidal salmonella serotypes cause typhoid fever. This discussion focuses on non-typhoidal salmonella, which causes an estimated 1.35 million illnesses and 420 deaths annually in the United States (CDC, 2022ae). For every confirmed positive lab test, an estimated 30 cases go unreported (CDC, 2022ad). Children under age 5 are more likely to become infected; this age group, adults over 65, and individuals who are immunocompromised are most likely to have severe infections (CDC, 2022ae).

Salmonella bacteria live in the intestinal tracts of humans, amphibians, reptiles, poultry, and other birds and in the feces of some animals (CDC, 2022ae) and infect individuals who do not wash their hands after contact with animals or animal feces. Salmonella can also be found in foods like chicken, turkey, beef, pork, eggs, fruits, and vegetables. Salmonellas contaminate an estimated one out of every 25 packages of supermarket chicken, infecting individuals if the contaminated chicken is not cooked thoroughly or if its juices leak onto surfaces or foods that are not cooked such as fruit and produce (CDC, 2022ad).

Salmonella illness, salmonellosis, results in a mild to severe diarrheal illness, acute gastroenteritis. Symptoms include sudden onset of diarrhea that may or may not be bloody, abdominal cramping, and fever. Less commonly, nausea, vomiting, and headache may be present. Diarrhea may last for days, increasing the risk of severe dehydration, especially in infants, young children, and older adults. Most individuals recover within seven days without antibiotic treatment; however, it can take months before bowel habits return to normal. Occasionally, salmonella infection can spread to other body areas, referred to as extra-intestinal infections, and it may be severe enough to cause disability and death (CDC, 2022ae).

Listeria Monocytogenes

The bacteria Listeria monocytogenes causes listeriosis, a serious but rare infection. In the United States, an estimated 1,600 individuals become ill with listeriosis each year, and 260 individuals die from it (CDC, 2023i). Listeriosis most often infects and sickens pregnant clients, their newborns, adults over 65, and individuals with weakened immune systems. Listeriosis is usually a mild illness in pregnant people, but it may cause severe disease in the fetus or newborn. Sometimes listeriosis becomes invasive—causing sepsis, meningitis, or encephalitis—and affects other parts of the body (CDC, 2023i).

Listeria bacteria are difficult to remove from food processing facilities, where they will spread to food that touches contaminated surfaces (CDC, 2023i). Refrigeration does not kill Listeria, but the bacteria is easily killed by heating food to a high enough temperature (CDC, 2023i). Foods more likely to be contaminated with Listeria include soft cheeses; deli products such as sliced cold cuts or cheese; deli salads such as coleslaw, potato salad, tuna salad, and chicken salad; sprouts; unpasteurized milk and associated products; hot dogs; and fermented or dry sausages such as chorizo, pepperoni, and salami (CDC, 2023i).

Listeriosis often results in fever and diarrhea, similar to other foodborne illnesses, but it is rarely diagnosed. More often, it is only identified if it becomes invasive or occurs during pregnancy. Signs of invasive listeriosis are meningitis-like symptoms of headache, nuchal rigidity, fever, confusion, and convulsions. Invasive listeriosis is serious, requiring inpatient hospital care; it causes death in one in five infected individuals (CDC, 2023i). Pregnant people often experience fever and flu-like symptoms; however, listeriosis can lead to miscarriage, stillbirth, premature delivery, or life-threatening infections of the newborn. Listeriosis during pregnancy results in a fetal loss in 20 percent of the cases and results in newborn death in about 3 percent of the cases (CDC, 2023i).

Escherichia Coli

Escherichia coli (E. coli) bacteria are normally found in human and animal intestines. While most are harmless, some may cause diarrhea, respiratory illness, and urinary tract or bloodstream infections ranging in severity (CDC, 2022k). Older adults, children under age 5, those with weakened immune systems, pregnant persons, and individuals who travel to certain countries are at higher risk for infection, although it can affect anyone (CDC, 2022k). The six types of pathogenic E. coli strains that cause diarrhea are often called diarrheagenic E. coli. Of this group, Shiga toxin-producing E. coli 0157 (STEC) is most commonly associated with foodborne outbreaks. An estimated 265,000 STEC infections occur in the United States each year; however, the actual number is likely higher as many infected individuals do not seek medical care and, if they do, may not have their stool tested (CDC, 2022j).

STEC is transmitted through ingestion of tiny amounts of human or animal feces, such as through contaminated food, unpasteurized milk, untreated water, or contact with cattle or with the feces of infected individuals. The CDC recommends avoiding unpasteurized milk, unpasteurized apple cider, and soft cheeses made from raw milk as these carry a high risk of STEC infection. Individuals have contracted infections by swallowing lake water while swimming, touching the environment in petting zoos, not washing hands after changing diapers, and eating food prepared by people who did not follow hand hygiene after using the restroom. In the United States in 2021 and 2022, there were a total of seven STEC outbreaks. These outbreaks were associated with prepared food items such as packaged salads, baby spinach, cake mix, frozen falafel, ground beef, and other unknown food sources (CDC, 2022j).

STEC infections often cause diarrhea (which may or may not be bloody), stomach cramps, vomiting, and low-grade fever. Symptoms usually last five to seven days with illness severity ranging from mild to life-threatening. Typically, individuals will begin to feel ill three to four days after ingesting STEC. Between 5 and 10 percent of individuals will develop hemolytic uremic syndrome (HUS), a condition that can lead to kidney failure, about a week after symptoms first appear when the diarrhea is improving (CDC, 2022k).

Lyme Disease

Lyme disease is the most commonly reported vector-borne illness in the United States, with approximately 300,000 annual infections (CDC, 2019i). It is most often found in the Upper Midwest, Northeast, and Mid-Atlantic, where it is spread by the Ixodes scapularis tick. The Ixodes pacificus tick is implicated in cases in northern California, Oregon, and Washington (CDC, 2022y). The geographic range of the ticks that spread Lyme disease is expanding, due in part to a changing landscape and climate (Johns Hopkins Bloomberg School of Public Health, n.d.).

Symptoms of early localized disease, within a month after the tick bite, include fever, chills, fatigue, headache, myalgias, arthralgia, lymphadenopathy, and erythema migrans (EM), a red, ring-shaped rash at the bite site that expands over several days, often to sizes greater than five centimeters in diameter with a central clearing that results in a “bull’s eye” appearance, although the rash can appear different on darker skin tones (Figure 13.4, Figure 13.5). EM occurs in up to 80 percent of those infected with Lyme, but the classic rash is not always present (CDC, 2022y). Untreated or undiagnosed early Lyme progresses to disseminated disease in about 60 percent of clients, with symptoms appearing months after the tick bite. Disseminated disease may present with skin, neurologic, cardiac, or rheumatologic manifestations. Performing serologic testing for Lyme disease is recommended when disseminated Lyme disease is being considered. However, clinical diagnosis is recommended over serologic testing for clients who present with an EM rash after frequenting an area where Lyme is common (CDC, 2022y).

In a study by Ly (2021), the researcher found that Black clients with Lyme disease seem to be diagnosed later in the disease process than White clients. Black clients are more often diagnosed with disseminated disease upon initial diagnosis and appear to be diagnosed outside of the months that Lyme disease is most frequently diagnosed, reinforcing the idea that they are diagnosed later in the disease process. A study by Palmiere et al. (2019) looked into missed and delayed Lyme diagnoses in dark-skinned populations of Appalachia with findings that echo the work by Ly. A potential reason for these missed or delayed diagnoses may be related to the varying appearance of EM in individuals with dark skin (Minority Nurse, 2013). The EM is an early sign of Lyme disease, whereas late symptoms include arthritis and neurological symptoms. Ly (2021) found that 34 percent of Black clients were diagnosed with neurological symptoms in comparison to only 9 percent of White clients, reinforcing the earlier diagnosis in White clients (Eldred, 2022; Ly, 2019). Another study showed similar findings among Black children—that they were less likely to be diagnosed with Lyme disease and were more likely to be diagnosed with the arthritis manifestations related to Lyme disease and not the skin or cutaneous manifestations (Hunt et al., 2023). It is imperative that nurses remain aware of the risks of Lyme disease in all clients and educate clients who are darker skinned on the signs and symptoms of Lyme disease to be aware of. Early diagnosis of Lyme disease and proper treatment with antibiotics usually results in a rapid and complete recovery (CDC, 2022y). Education on tick bite prevention and tick removal can help prevent spread of the disease.

Figure 13.4 A bull’s-eye rash (erythema migrans) is often a characteristic sign of Lyme disease. (credit: CDC, Public Domain)

Figure 13.5 The appearance of erythema migrans can vary and appear different on dark skin tones, which may be a factor in the late diagnosis of Lyme disease in individuals with darker skin. (credit: modification of work by CDC, Public Domain)

West Nile Virus

Spread by the bite of an infected mosquito, the West Nile virus (WNV) is the leading cause of mosquito-borne disease in the United States. The disease is now considered native to the United States, with outbreaks reported each summer through the fall (CDC, 2019i). Mosquitos become infected with WNV by feeding on infected birds and then spread it to people and animals by biting them. In rare cases, WNV has been spread through blood transfusion, organ transplant, and perinatal transmission from mother to baby during pregnancy, delivery, or breastfeeding. It is not spread through droplets, by touching live animals or birds, or by eating infected animals (CDC, 2022am).

Although most infected individuals have no symptoms, one in five experiences fever, headache, body aches, vomiting, and diarrhea. Serious, sometimes fatal, disease occurs in one out 150 infected individuals, and of this group, one out of 10 die (CDC, 2022am). This severe infection often affects the central nervous system (neuroinvasive disease), causing encephalitis, acute flaccid paralysis, or meningitis. Recovery can take several months, and some effects may be permanent (CDC, 2022am).

WNV should be considered in any client with a febrile or acute neurologic illness with a recent exposure to mosquitos, blood transfusion, or organ transplant (CDC, 2023c). Lab diagnosis can be accomplished by testing the cerebrospinal fluid (CSF) and detecting WNV-specific IgM antibodies. Viral cultures and reverse transcriptase-polymerase chain reaction tests can be performed on blood specimens and confirm infection (CDC, 2023c). This is a nationally notifiable condition, a disease that, by law, must be reported to government authorities, allowing for case surveillance to assess transmission patterns and determine interventions to control outbreaks. Local and federal laws and regulations determine which diseases and conditions must be reported for case surveillance (CDC, 2022v). This will be discussed in more detail in the next section, Infectious Disease Prevention and Control.

Zika Virus

The Zika virus is caused by infected Aedes aegypti and Aedes albopictus mosquitoes found throughout the United States (CDC, 2019i). It can be passed from a pregnant person to their fetus, and fetal infection during pregnancy may cause birth defects such as microcephaly and other severe fetal brain defects (CDC, 2022aq). Zika can also be passed from an infected person via sexual activity including vaginal, anal, and oral sex and sharing sex toys, but male and female condoms can reduce this risk. Sexual transmission is especially concerning as many individuals infected with Zika are asymptomatic and may be unaware they are infected. Blood or urine tests can confirm infection. In 2015–2016, a large outbreak of travel-associated Zika cases occurred in the United States, along with local transmission cases of Zika in Florida and Texas. In 2017, the number of Zika cases in the United States started to decline, and no cases of Zika transmission by mosquitos have been reported since 2018; however, Zika remains a global health threat (CDC, 2022aq).

Clinical findings in symptomatic disease include acute onset of fever with maculopapular rash, arthralgia, or conjunctivitis (CDC, 2019m). Other symptoms may include myalgias and headaches with clinical illness lasting a week or less. Zika infection during pregnancy causes severe fetal brain defects, including microcephaly, a condition where a baby’s head is much smaller than expected, often resulting in abnormal brain development. Infants born to individuals with Zika infection during pregnancy must be evaluated for congenital infection and neurologic abnormalities (CDC, 2019m). Zika is a nationally notifiable condition reported to state and local health departments. No specific treatment for Zika exists as it is supportive in nature including rest, fluids, and use of analgesics or antipyretics. Those who are infected should be protected from further mosquito exposure for a few days after illness to prevent transmission to other mosquitos, thereby reducing the risk of local transmission (CDC, 2022aq).

Malaria

A mosquito-borne disease, malaria is caused by a parasite (Plasmodium falciparum, P. vivax, P. ovale, P. malariae, and P. knowlesi) that frequently infects the Anopheles mosquito and is then transmitted to humans through this infected mosquito’s bite (CDC, 2022z). It can also be transmitted through a blood transfusion, through an organ transplant, perinatally, or by sharing needles contaminated with blood. Malaria can result in serious illness and death (CDC, 2022z). P. falciparum causes the most severe malaria and is common in many African countries. Individuals living in poverty or rural areas lacking access to health care are at the greatest risk for life-threatening illness (CDC, 2022z). An estimated 241 million malaria cases occurred globally in 2020, with over 600,000 deaths. An estimated 90 percent of these deaths occurred in children under age 5 in sub-Saharan Africa, where the disease perpetuates a cycle of disease and poverty (CDC, 2022z). Almost half of the world’s population is at risk for malaria, and lower-income countries are disproportionately affected (WHO, 2023a). Within the United States, approximately 2,000 cases are diagnosed yearly, with most cases occurring in immigrants and travelers returning from countries where malaria is endemic, such as sub-Saharan Africa and South Asia (CDC, 2022z).

Clinical findings in acute malaria include flu-like symptoms of fever, chills, headache, myalgias, fatigue, GI symptoms, and sometimes anemia and jaundice. Untreated malaria may cause kidney failure, seizures, mental status changes, coma, and death. P. vivax and P. ovale may result in relapsing malaria because these parasites can remain dormant in the liver and then come out of hibernation, resulting in acute illness (CDC, 2022z). Available malaria treatments are highly effective when started at the onset of symptoms (CDC, 2022z). Malaria is a nationally notifiable condition that must be reported to state health departments and the CDC through the National Malaria Surveillance System (NMSS). The CDC investigates locally transmitted malaria, such as transfusion malaria, and supports health professionals in preventing, diagnosing, and treating malaria (CDC, 2020a). In June 2023, the CDC issued a health alert advisory notifying clinicians, public health authorities, and the general public about the identification of a handful of cases of locally acquired P. vivax malaria in Florida and one in Texas (CDC, 2023j). This was the first time in 20 years that a case of locally acquired malaria was identified in the United States. Although the risk of locally acquired malaria remains low, vigilance is needed to prevent mosquito bites (CDC, 2023j).

Legionnaires’ Disease

Legionnaires’ disease is a dangerous type of pneumonia caused by Legionella bacteria. Normally found in lakes and streams, Legionella become a health concern when they grow and spread in water systems, such as sink faucets, centralized building cooling towers, decorative fountains, hot water tanks, and heaters. As Legionella grow and reproduce, water containing the bacteria can spread in droplets (CDC, 2021f). Individuals can also become ill by aspirating drinking water containing Legionella. Legionnaires’ disease symptoms often begin within two weeks post exposure, are similar to other types of pneumonia, and include cough, shortness of breath, fever, myalgias, and headaches; some individuals experience diarrhea, nausea, and confusion (CDC, 2021f). While easily treated with antibiotics, Legionnaire’s disease causes death in one in 10 individuals who contract it (CDC, 2021f).

Cryptosporidium

Cryptosporidium (Crypto) is a microscopic parasite that causes cryptosporidiosis, a diarrheal disease. Protected by an outer shell, the parasite can survive outside a host’s body for long time periods and avoid disinfection with chlorine (CDC, 2019j). Crypto parasites are found worldwide and in every U.S. region, where an estimated 823,000 cases occur each year. Anyone can become sick with crypto, but individuals who are immunocompromised are more likely to have severe symptoms (CDC, 2019j). High-risk populations include children attending childcare centers, childcare workers, older adults, hikers who drink unfiltered and untreated water, individuals who drink from untreated shallow wells, swimmers, individuals who handle infected cattle, and international travelers (CDC, 2019j).

Crypto is transmitted by the fecal-oral route. The parasites live in an infected host’s intestines; the host will shed millions of Crypto parasites in a bowel movement. Many community outbreaks have been linked to consuming municipal or recreational water (CDC, 2019j). Causes of cryptosporidiosis may include:

• Swallowing recreational water contaminated with crypto
• Drinking water contaminated by stool from an infected individual
• Swallowing something that has come in contact with an infected individual’s stool
• Touching the mouth with hands after coming in contact with an infected individual’s stool (CDC, 2019j)

Symptoms of cryptosporidiosis begin about a week following infection and include watery diarrhea, stomach cramping, dehydration, nausea, vomiting, fever, and weight loss; they usually persist for one to two weeks. Those who are immunocompromised may develop a more severe and sometimes fatal illness. Healthy individuals generally recover without treatment.

Chlamydia

Caused by infection with Chlamydia trachomatis, chlamydia is the most frequently reported bacterial STI, resulting in cervicitis, urethritis, and proctitis. In 2018, there were an estimated 4 million chlamydia infections in the United States (CDC, 2022c). Many individuals are asymptomatic and do not seek testing. Screening is necessary to identify most infections and can reduce the rates of adverse outcomes in women. In women, untreated infections can lead to pelvic inflammatory disease (PID), tubal infertility, ectopic pregnancy, and chronic pelvic pain (CDC, 2022c). In men, untreated infections rarely result in major health problems but may cause infertility. Chlamydial infections are most common in young people ages 15 to 24 and BIPOC individuals. In 2020, chlamydia rates for Black individuals were six times the rate seen in White individuals (CDC, 2022c).

Chlamydia is transmitted via vaginal, anal, or oral sex with an infected partner. Ejaculation is not necessary to transmit the infection. It can infect the pharynx, cervix, urethra, upper reproductive tract, rectum, and conjunctiva. Symptoms in women may include abnormal vaginal discharge and dysuria. Symptoms may include penile discharge, dysuria, and pain and swelling in one or both testicles in men. Symptoms of rectal chlamydia may include rectal pain, discharge, and bleeding. Pregnant individuals can pass chlamydia to their baby during childbirth, resulting in pre-term delivery, conjunctivitis, and pneumonia in the neonate (CDC, 2022c).

When used correctly and with each sexual encounter, condoms can reduce the risk of chlamydia. Avoiding oral, vaginal, and anal sex is the only way to prevent chlamydia. Being in a mutually monogamous relationship with a partner who does not have chlamydia also lowers one’s risk (CDC, 2022c).

Gonorrhea

Caused by Neisseria gonorrhoeae, gonorrhea is the second most commonly reported bacterial STI. Approximately 1.6 new infections occurred in the United States in 2018, with more than half among individuals ages 15 to 24. Because many infections are asymptomatic, the true number of cases may be much higher than reported (CDC, 2022o). Any sexually active individual can become infected, but most cases are among teenagers, young adults, and Black individuals (CDC, 2022o).

Gonorrhea is transmitted via sexual contact with the penis, vagina, mouth, or anus of an infected partner. Ejaculation is not needed for transmission. It infects the mucous membranes of the reproductive tract in women and of the mouth, throat, eyes, and rectum of both men and women (CDC, 2022o). Gonorrhea can also be spread during childbirth. Infection in newborns may result in blindness, joint infection, or sepsis; treatment of gonorrhea in pregnant individuals reduces the risk of these complications.

Symptoms in women are often mild, nonspecific, and mistaken for bladder or vaginal infections. Initial symptoms include dysuria, increased vaginal discharge, and bleeding between menses. Symptoms in men occur one to 14 days after infection and include dysuria; white, yellow, or green urethral discharge; and potential testicular or scrotal pain indicative of concomitant epididymitis, a complication of urethral infection (CDC, 2022o). Rectal infection may also be asymptomatic or cause discharge, anal itching, pain, bleeding, or painful bowel movements. Pharyngeal infection may result in a sore throat or may be asymptomatic (CDC, 2022o). Complications of gonorrhea include PID in women, which may lead to chronic pelvic pain, infertility, or increased risk of ectopic pregnancy. In men, complications include epididymitis and infertility. Untreated gonorrhea can potentially spread to the blood, resulting in disseminated gonococcal infection (DGI), a life-threatening infection characterized by arthritis, tenosynovitis, and dermatitis (CDC, 2022o).

When used correctly and with every sexual encounter, latex condoms reduce the risk of gonorrhea. Avoiding oral, vaginal, and anal sex is the surest way to prevent gonorrhea. Being in a long-term, mutually monogamous relationship with a partner who does not have gonorrhea is another way to lower one’s risk (CDC, 2022o).

Syphilis

Rates of syphilis, a bacterial STI caused by Treponema pallidum, have steadily risen over the past 20 years. In 2021, the United States reported 176,713 cases, an approximately 73 percent increase over a four-year period (CDC, 2022ak). MSM accounted for 43 percent of all primary and secondary cases, but cases are increasing among heterosexual individuals. Congenital syphilis, another growing concern, occurs when a pregnant person passes syphilis to the fetus. Over 2,800 cases of congenital syphilis were reported in 2021, a 185 percent increase since 2017 (CDC, 2022ak).

Syphilis spreads through direct contact with a syphilitic chancre (sore) that is usually located on or around the penis, vagina, anus, rectum, lips, or mouth (CDC, 2022ak). It is also transmitted during vaginal, anal, or oral sex and pregnancy. When a pregnant client has syphilis, the infection can spread to the fetus, resulting in a high risk of stillbirth or death shortly after birth. Untreated syphilis in pregnant clients results in infant death in up to 40 percent of cases (CDC, 2022ak). A newborn with congenital syphilis may be asymptomatic, but without immediate treatment, serious problems such as developmental delays, seizures, and death may ensue (CDC, 2022ak).

Often beginning three weeks after initial infection, symptoms may resemble those of many other diseases, yet they follow a typical progression, with each stage potentially lasting for weeks, months, or years. At any stage of infection, syphilis can invade the nervous system (neurosyphilis), the visual system (ocular syphilis), and the auditory and vestibular systems (otosyphlis). The four stages are as follows:

• The primary stage starts with a single or multiple firm, round, painless chancres located where syphilis entered the body that last three to six weeks and then heal, regardless of treatment. Without treatment, syphilis will progress to the secondary stage (CDC, 2022ak).
• In the secondary stage, lesions develop in the mouth, vagina, or anus, and skin rashes that are not usually itchy and may appear as rough red or reddish-brown spots appear on the palms of the hands and soles of the feet. They can be very faint, making them difficult to see. Condyloma lata—large, raised gray or white lesions—may develop in moist, warm areas such as the mouth, axilla, and groin. Other symptoms are fever, swollen lymph nodes, sore throat, headaches, weight loss, myalgias, fatigue, and patchy hair loss. These symptoms will resolve with or without treatment, but an untreated infection will progress to the latent and potentially tertiary stage of disease (CDC, 2022ak).
• In the latent stage, there are no visible symptoms, and without treatment, it will remain in the body. This stage can last for years.
• Tertiary syphilis may develop in some untreated syphilis infections, appearing 10 to 30 years after initial infection and affecting multiple organ systems. This stage is rare, but it can be fatal.

Condoms, when used correctly, can reduce the risk of syphilis; however, transmission can occur if the condom does not cover the lesions. Avoiding oral, vaginal, and anal sex is the only way to avoid syphilis. Being in a mutually monogamous relationship with a partner who does not have syphilis is another way to lower one’s risk of getting syphilis (CDC, 2022ak).