Chapter 3Infectious Diseases Related To Travel
Kashmira Date, Eric Mintz
Cholera is an acute bacterial, intestinal infection caused by toxigenic Vibrio cholerae O-group 1 or O-group 139. Many other serogroups of V. cholerae, with or without the cholera toxin gene (including the nontoxigenic strains of the O1 and O139 serogroups), can cause a cholera-like illness. Only toxigenic strains of serogroups O1 and O139 have caused widespread epidemics and are reportable to the World Health Organization (WHO) as “cholera.”
V. cholerae O1 has 2 biotypes, classical and El Tor, and each biotype has 2 distinct serotypes, Inaba and Ogawa. The symptoms of infection are indistinguishable, although more people infected with the El Tor biotype remain asymptomatic or have only a mild illness. In recent years, infections with the classical biotype of V. cholerae O1 have become rare and are limited to parts of Bangladesh and India.
MODE OF TRANSMISSION
Toxigenic V. cholerae O1 and O139 are free-living bacterial organisms found in fresh and brackish water, often in association with copepods or other zooplankton, shellfish, and aquatic plants. Cholera infections are most commonly acquired from drinking water in which V. cholerae is found naturally or into which it has been introduced from the feces of an infected person. Other common vehicles include contaminated fish and shellfish, produce, or leftover cooked grains that have not been properly reheated. Transmission from person to person, even to health care workers during epidemics, is rarely documented.
Since 1961, the seventh pandemic of cholera, caused by V. cholerae serogroup O1, biotype El Tor, has spread from Indonesia through most of Asia into Eastern Europe and Africa, and from North Africa to the Iberian Peninsula. In 1991, an extensive epidemic began in Peru and spread to neighboring countries in the Western Hemisphere. Although few cases of cholera occur in South or Central America, V. cholerae O1 remains endemic in much of Africa and South and Southeast Asia. V. cholerae O139 spread rapidly through Asia in the early 1990s but has since remained localized to a few areas in Bangladesh and India.
In 2009, 45 countries reported 221,226 cholera cases and 4,946 cholera deaths (case-fatality ratio, 2.24%) to WHO. Resource-poor areas report the most cases; 98% of cases and 99% of deaths were reported from Africa. Cholera has the potential to emerge in dramatic epidemics, as was seen with the massive outbreaks that affected Zimbabwe in 2008 and 2009, with close to 100,000 cases and over 4,000 deaths reported. More recently, in October 2010, a cholera outbreak was confirmed in Haiti, within months of the devastating earthquake that destroyed the Haitian capital of Port-au-Prince and surrounding areas. As of early November 2010, nearly 17,000 hospitalized cases and more than 1,000 deaths had been reported. Consequent to the lack of safe water infrastructure in Haiti and additional destruction caused by the earthquake, the number of cases and deaths is expected to continue to increase in Haiti, and travel-associated cases may appear in other Caribbean nations and in the United States.
From 1999 through 2008, 60 confirmed cases of cholera in the United States were acquired abroad. Travelers who follow the usual tourist itineraries and who observe safe food and water recommendations and hygiene precautions while in countries reporting cholera have virtually no risk. The risk is increased for those who drink untreated water, do not follow proper hygiene recommendations, or eat poorly cooked or raw food, especially seafood, in endemic or outbreak settings.
Two reports of cholera have been associated with food served on board international flights, most recently in 1992, during the Latin American epidemic, on a flight from Argentina to Los Angeles. CDC consequently advised the International Air Transport Association that oral rehydration solutions should be carried on international flights and that certain food items prepared in cities with cholera epidemics should not be served. Airline flights have not been implicated in any subsequent cases of cholera.
Cholera infection is most often asymptomatic or results in a mild gastroenteritis. Severe cholera is characterized by acute, profuse watery diarrhea, described as “rice-water stools,” and often vomiting, leading to volume depletion. Signs and symptoms include tachycardia, loss of skin turgor, dry mucous membranes, hypotension, and thirst. Additional symptoms, including muscle cramps, are secondary to the resulting electrolyte imbalances. If untreated, volume depletion can rapidly lead to hypovolemic shock and death.
Cholera is confirmed through culture of a stool specimen or rectal swab. Cary-Blair medium is ideal for transport, and the selective thiosulfate-citrate-bile salts (TCBS) agar is ideal for isolation and identification. Reagents for serogrouping V. cholerae isolates are available in all state health department laboratories. Commercially available rapid test kits do not yield an isolate for antimicrobial susceptibility testing and subtyping and should not be used for routine diagnosis. All isolates should be sent to CDC via state health department laboratories for cholera toxin testing and subtyping. Cholera is a nationally reportable disease.
Rehydration is the cornerstone of therapy. Oral rehydration salts and, when necessary, intravenous fluids and electrolytes, if administered in a timely manner and in adequate volumes, will reduce case-fatality ratios to well under 1%. Antibiotics reduce fluid requirements and duration of illness. Antimicrobial therapy is indicated for severe cases, which can be treated with tetracycline, doxycycline, furazolidone, erythromycin, or ciprofloxacin. When possible, antimicrobial susceptibility testing should inform treatment choices.
PREVENTIVE MEASURES FOR TRAVELERS
Safe food and water precautions and frequent handwashing are critical in preventing cholera (see Chapter 2, Food and Water Precautions). Chemoprophylaxis is not indicated.
No cholera vaccine is available in the United States. Two oral vaccines are available outside the United States: Dukoral (Crucell, the Netherlands) and Shanchol (Shantha Biotechnics, India)/mORCVAX (Vabiotech, Vietnam). Shanchol and mORCVAX are similar vaccines produced by different manufacturers. These vaccines appear to be safe, provide better immunity, and have fewer adverse effects than the previously licensed injectable vaccine. However, CDC does not recommend these vaccines for most travelers because of the low risk of cholera to US travelers and the incomplete immunity that the vaccines confer. No country or territory requires vaccination against cholera as a condition for entry.
Further information on Dukoral can be obtained from Crucell (www.crucell.com). Information on Shanchol can be obtained from Shantha Biotechnics (www.shanthabiotech.com, 516-859-3010 [United States], 91-40-23234136 [India], email@example.com). Information on mORCVAX can be obtained from Vabiotech (www.vabiotechvn.com/english, 84-4-9717710 [Vietnam]).
- CDC. Cholera associated with an international airline flight, 1992. MMWR Morb Mortal Wkly Rep. 1992 Feb 28;41(8):134–5.
- CDC. Cholera outbreak—Haiti, October 2010. MMWR Morb Mortal Wkly Rep. 2010 Nov 5;59(43):1411.
- CDC. Two cases of toxigenic Vibrio cholerae O1 infection after Hurricanes Katrina and Rita—Louisiana, October 2005. MMWR Morb Mortal Wkly Rep. 2006 Jan 20;55(2):31–2.
- CDC. Update: cholera outbreak—Haiti, 2010. MMWR Morb Mortal Wkly Rep. 2010 Nov 19;59(45):1473–9.
- Gaffga NH, Tauxe RV, Mintz ED. Cholera: a new homeland in Africa? Am J Trop Med Hyg. 2007 Oct;77(4):705–13.
- Griffith DC, Kelly-Hope LA, Miller MA. Review of reported cholera outbreaks worldwide, 1995–2005. Am J Trop Med Hyg. 2006 Nov;75(5):973–7.
- Sack DA, Sack RB, Nair GB, Siddique AK. Cholera. Lancet. 2004 Jan 17;363(9404):223–33.
- Sutton RG. An outbreak of cholera in Australia due to food served in flight on an international aircraft. J Hyg (Lond). 1974 Jun;72(3):441–51.
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