(Vibrio cholerae)

Clinical Manifestations

Cholera is characterized by painless voluminous watery diarrhea without abdominal cramps or fever. Dehydration, hypokalemia, metabolic acidosis, and occasionally, hypovolemic shock can occur in 4 to 12 hours if fluid losses are not replaced. Coma, seizures, hypoglycemia, and death also can occur, particularly in children. Stools are colorless, with small flecks of mucus ("rice-water"), and contain high concentrations of sodium, potassium, chloride, and bicarbonate. Most infected people with toxigenic Vibrio cholerae O1 have no symptoms, and some have only mild to moderate diarrhea lasting 3 to 7 days; fewer than 5% have severe watery diarrhea, vomiting, and dehydration (cholera gravis).

Etiology

V cholerae is a gram-negative, curved, motile bacillus with many serogroups. Only serogroups O1 and O139 cause epidemic clinical cholera associated with enterotoxin. There are 3 serotypes of V cholerae O1: Inaba, Ogawa, and Hikojima. The 2 biotypes of V cholerae are classical and El Tor. El Tor is more commonly observed. Since 1992, toxigenic V cholerae serogroup O139 has been recognized as a cause of cholera in Asia. Nontoxigenic strains of V cholerae O1 and some toxigenic non-O1 serogroups (eg, 0141) can cause sporadic diarrheal illness, but they have not caused epidemics.

Epidemiology

During the last 5 decades, V cholerae O1 biotype El Tor has spread from India and Southeast Asia to Africa, the Middle East, Southern Europe, and the Western Pacific Islands (Oceania). In 1991, epidemic cholera caused by toxigenic V cholerae O1, serotype Inaba, biotype El Tor, appeared in Peru and spread to most countries in South, Central and North America. In the United States, cases resulting from travel to or ingestion of contaminated food transported from Latin America or Asia have been reported. In addition, the Gulf Coast of Louisiana and Texas has an endemic focus of a unique strain of toxigenic V cholerae O1. Most cases of disease from this strain have resulted from consumption of raw or undercooked shellfish.

Humans are the only documented natural host, but free-living V cholerae organisms can exist in the aquatic environment. The usual mode of infection is ingestion of large numbers of organisms from contaminated water or food (particularly raw or undercooked shellfish, raw or partially dried fish, or moist grains or vegetables held at ambient temperature). Direct person-to-person spread has not been documented. People with low gastric acidity and with blood group O are at increased risk of cholera infection.

The incubation period usually is 1 to 3 days, with a range of a few hours to 5 days.

Diagnostic Tests

V cholerae can be cultured from fecal specimens or vomitus plated on thiosulfate citrate bile salts sucrose agar. Because most laboratories in the United States do not culture routinely for V cholerae or other Vibrio organisms, clinicians should request appropriate cultures for clinically suspected cases. Isolates of V cholerae should be sent to a state health department laboratory for serogrouping; isolates of serogroup O1 or O139 then are sent to the Centers for Disease Control and Prevention (CDC) for testing for production of enterotoxin. A fourfold increase in vibriocidal antibody titers between acute and convalescent serum specimens or a fourfold decrease in vibriocidal titers available through CDC laboratories between early and late convalescent (more than a 2-month interval) serum specimens can confirm the diagnosis.

Treatment

Oral or parenteral rehydration therapy to correct dehydration and electrolyte abnormalities is the most important modality of therapy and should be initiated as soon as the diagnosis is suspected.¹ Oral rehydration is preferred unless the patient is in shock, is obtunded, or has intestinal ileus. The World Health Organization's Oral Rehydration Solution (ORS) has been the standard, but data suggest that rice-based ORS or amylase-resistant starch ORS is more effective.

Antimicrobial therapy results in prompt eradication of vibrios, decreases the duration of diarrhea, and decreases fluid losses. Antimicrobial therapy should be considered for people who are moderately to severely ill. Oral doxycycline as a single dose or tetracycline for 3 days are the drugs of choice for cholera. Although tetracyclines generally are not recommended for children younger than 8 years of age, in cases of severe cholera, the benefits may outweigh the small risk of staining of developing teeth (see Antimicrobial Agents and Related Therapy). If strains are resistant to tetracyclines, then ciproflaxin, ofloxacin, or trimethoprim-sulfamethoxazole can be used. Antimicrobial susceptibility testing of newly isolated organisms should be determined.

Isolation of the Hospitalized Patient

In addition to standard precautions, contact precautions are indicated for diapered or incontinent children for the duration of illness.

Control Measures

Hygiene

Disinfection or boiling of water prevents transmission. Thoroughly cooking crabs, oysters, and other shellfish from the Gulf Coast before eating is recommended to decrease the likelihood of transmission. Foods such as fish, rice, or grain gruels should be refrigerated promptly after meals and thoroughly reheated before eating. Appropriate hand hygiene after defecating and before preparing or eating food is important for preventing transmission.

Treatment of Contacts

The administration of doxycycline, tetracycline, ciprofloxacin, ofloxacin, or trimethoprim-sulfamethoxazole within 24 hours of identification of the index case may prevent coprimary cases of cholera among household contacts. However, because secondary transmission of cholera is rare, chemoprophylaxis of contacts is not recommended by the World Health Organization, except in special circumstances in which the probability of fecal exposure is high and the medication can be delivered rapidly.

Vaccine

No cholera vaccines are available in the United States. An oral vaccine is available in other countries (Dukoral from SBL vaccines in Sweden). Cholera immunization is not required for travelers entering the United States from cholera-affected areas, and the World Health Organization no longer recommends immunization for travel to or from areas with cholera infection. No country requires cholera vaccine for entry.

Reporting

Confirmed cases of cholera must be reported to health authorities in any country in which they occur or were contracted. Local and state health departments should be notified immediately of presumed or known cases of cholera attributable to V cholerae O1 or O139.