July 07, 2014
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Effective surveillance led to control of 2013 cholera outbreak in Mexico

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Ongoing microbiologic surveillance of Vibrio cholerae infection in Mexico successfully controlled an outbreak in the La Huasteca region within 13 weeks, according to recent findings.

In an MMWR report, researchers characterized an outbreak of V. cholerae serogroup O1, serotype Ogawa, biotype El Tor, which occurred in September in Mexico.

The first two cases of cholera were identified on Sept. 2 and 6 by Mexico’s National Epidemiological Surveillance System. The cases were confirmed via rectal swab cultures. Additional analysis revealed that the strains were identical to each other but different from strains that previously circulated in Mexico. These strains were also indistinguishable from the strain that led to outbreaks in Haiti, the Dominican Republic and Cuba. The strain was vulnerable to doxycycline, moderately susceptible to ampicillin and chloramphenicol, had less than complete susceptibility to ciprofloxacin, and resistant to furazolidone and trimethoprim-sulfamethoxazole. Investigators were unable to determine a common source of infection, identify any additional cases or find any epidemiologic links between the cases. Both patients’ symptoms resolved after they were treated with a single, 300-mg dose of doxycycline.

On Sept. 12 and 13, the Hidalgo County Health Department reported four cases of cholera among residents of the La Huasteca region, which is roughly 75 miles east of Mexico City. Between Sept. 19 and Dec. 14, 175 cases of cholera were confirmed in La Huasteca. WHO guidelines were used to characterize and classify these cases. Cases were categorized as suspected cholera if, in an area where the disease was not known to exist, a patient aged at least 5 years exhibited severe dehydration or died of acute watery diarrhea. Cases were laboratory confirmed at the Instituto de Diagnostico y Referencia Epidemiológicos in Mexico City.

The investigators found that of the 175 cases, 49% were female (median age, 32 years). Twenty-three percent of patients needed to be admitted to a hospital, with an average stay of 36 hours. All patients had acute and watery diarrhea, with 46 (26%) having “rice-water” stool. According to the investigators, 36% of patients had fewer than five bowel movements within 24 hours, 49% experienced vomiting and 17% had cramps. Forty-three percent of patients showed some degree of dehydration, with mild dehydration (<5% loss of body weight) noted in 21% of patients, moderate dehydration (6%-9% loss of body weight) observed in 18% of patients and severe dehydration (≥10% loss) noted in only 3% of patients. There was one death — a 67-year-old female patient with a history of diabetes and chronic renal failure. Rapid diagnosis and treatment of the La Huasteca outbreak was facilitated by a mobile microbiology laboratory.

Sporadic cases of infection by the V. cholerae serogroup O1 have been seen in Mexico since the conclusion of an outbreak that occurred between 1991 and 2001. During this outbreak, there were 45,062 confirmed cases, with a 1.1% case-fatality rate. Regular, active surveillance since then enabled the confirmation of one case in 2010, one in 2011 and two cases in 2012.

Currently, in Mexico, health professionals at all levels of the health care system are being trained in the prevention, treatment and control of the disease. Additionally, public awareness campaigns are being implemented to ensure food and water quality, and efforts toward improved water sanitation are being implemented. Moreover, surveillance is ongoing and focused on V. cholerae infection and reservoir contamination.

“As a result of these actions, the outbreak in La Huasteca, in which samples from 88% of the cases were collected, was controlled within the first 13 weeks,” the researchers wrote. “Ongoing and continuous microbiologic surveillance of area reservoirs and laboratory investigation of all cases of acute diarrhea have not detected any new cases of cholera since December 17, 2013.”

Disclosure: The researchers report no relevant financial disclosures.