Understanding Cholera: A Threat Still Today

Cholera Overview

Causative Agent

Cholera is toxigenic Vibrio cholerae serogroups O1 and O139 severe enteric infection. Although other serogroups (non-toxigenic O1 and O139 strains) can cause cholera-like disease, only toxigenic O1 and O139 strains result in large outbreaks and are reportable to the World Health Organization (WHO) as "cholera." The pandemic that started in 1961 and currently circulates worldwide is caused by the O1 serogroup. O139, which was once predominant in Asia, is now rarely reported.

V. cholerae O1 occurs in two biotypes—Classical and El Tor—each of three serotypes: Inaba, Ogawa, and Hikojima only infrequently. The El Tor biotype is pan-world and produces milder or asymptomatic infections than Classical. Hybrid strains with traits of both biotypes are now common and may be more virulent.

Transmission

Natural reservoirs of cholera bacteria are fresh and brackish water, usually found in relation to plankton, shellfish, and aquatic vegetation. Infection in man most commonly results from ingestion of contaminated water or food—especially raw or inadequately cooked seafood. Transmission by direct contact with infected individuals or fomites, primarily in hospitals, occurs.

Cholera epidemics are typically caused by poor sanitation, and climatic occurrences like floods or hurricanes. Those who travel with strict hygiene, consume secure food and water, and maintain sanitation measures are at low risk.

Epidemiology

Between 2017 and 2022, the United States diagnosed 39 cases of cholera in recent foreign travelers, primarily from South Asia and Africa. Pakistan, India, and Kenya were the most visited countries. Cases that arose from travel decreased during the COVID-19 pandemic but were seen in higher numbers in 2022. To date, as of 2023, WHO has declared cholera a Grade 3 emergency after outbreaks in over 29 countries.

Cholera continues to be endemic in approximately 50 nations, predominantly in South and Southeast Asia and Africa. Risk is heightened in areas where there is poor access to clean water or sanitation, or in the event of humanitarian emergencies. Persons with decreased stomach acid or blood group O are at greater risk for severe disease.

Clinical Features

Cholera typically causes watery diarrhea (typically "rice water stools") with no fever. Vomiting, nausea, and dehydration quickly follow this. In severe illness, in ~10% of the infections, there can be hypovolemic shock and sudden death if not treated. With prompt rehydration, the mortality is less than 1%.

Diagnosis

Diagnosis in secondary travelers should be provided in acute watery diarrhea with recent history of travel to cholera-endemic areas. Rapid diagnostic tests (RDTs) will detect O1 and O139 antigens but not yield cultures for toxin detection or antibiotic susceptibility testing. Confirmatory testing is by stool culture and by molecular assays such as PCR. Isolates should be submitted to public health laboratories and CDC for full characterization. Cholera is a nationally notifiable condition in the U.S.

Treatment

Rehydration is the cornerstone of cholera treatment. Oral rehydration solution (ORS) is standard, with IV fluid for severe disease. Antibiotics can shorten the course of illness and are reserved for severe illness or high-risk patients. In recent US isolates (2017–2019), the majority were ciprofloxacin-resistant but susceptible to azithromycin and tetracycline. Zinc supplementation is beneficial in children to reduce severity of illness and duration.

Prevention

Food and Water Safety

Strict hygiene practices and food/water precautions should be used by the traveler. Routine antibiotic prophylaxis is not recommended.

Vaccination

The oral cholera vaccine CVD 103-HgR (Vaxchora) is licensed by the FDA for individuals 2–64 years of age traveling to destinations with active cholera transmission (regions with recent or ongoing outbreaks caused by toxigenic O1 strains). Routine use in most US travelers is not recommended.

Vaccine Use

Administration: Single oral dose ≥10 days before potential exposure. Children aged 2–5 years receive half-volume dose (50 mL).

Efficacy: In adults, 90% at 10 days and 80% at 3 months. Over 97% of children aged 2–17 years developed immune response within 11 days.

Restrictions: Not indicated for individuals <2 or >64 years, pregnant, lactating, or immunocompromised individuals.

Side Effects: Mild symptoms like nausea, headache, or tiredness were common. Serious adverse events were rare.

Precautions

Vaxchora should not be given to individuals with known allergies to its components or those who have taken antibiotics in the prior 14 days. Chloroquine may reduce vaccine effectiveness and should be started ≥10 days post-vaccination. The vaccine strain may be shed in stool for a week, so caution is advised around immunocompromised individuals. Medical attention is advised where symptoms manifest and persist.