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Notes from the Field: Identification of Vibrio cholerae Serogroup O1, Serotype Inaba, Biotype El Tor Strain — Haiti, March 2012

On October 20, 2010, an outbreak of cholera was confirmed in Haiti for the first time in more than a century. As of April 10, 2012, a total of 534,647 cases, 287,656 hospitalizations, and 7,091 deaths have been reported in Haiti as a result of the outbreak (1). The Vibrio cholerae strain that caused the Haiti epidemic has been characterized as toxigenic V. cholerae, serogroup O1, serotype Ogawa, biotype El Tor (2).

Recently, two V. cholerae isolates collected on March 12 and 13, 2012, in Anse Rouge, Artibonite Department, were characterized at the National Public Health Laboratory in Haiti as non-Ogawa serotypes. The isolates subsequently were confirmed by CDC to belong to the Inaba serotype. By molecular analyses (pulsed-field gel electrophoresis, multilocus variable number of tandem repeat analysis, and virulence gene sequencing [ctxB and tcpA]), these two isolates are indistinguishable from the currently circulating V. cholerae serotype Ogawa strain in Haiti. The molecular analyses conducted to date suggest that they arose from serotype switching, which is a commonly observed phenomenon in cholera epidemics, often driven by population immunity to the circulating serotype. Further characterization efforts are ongoing. Finding these two isolates does not change current clinical management guidelines (3).

Ogawa and Inaba serotypes do not appear to differ in the severity or duration of illness they cause; most persons infected with V. cholerae of either serotype will not develop clinically apparent disease. Type-specific immunity is induced by infection; however, cross-protective immunity between the two serotypes is incomplete (4). Previous studies have indicated that the Ogawa serotype offers less protective immunity than Inaba from reinfection with the heterologous serotype (5). Thus, if the Inaba strain becomes established in Haiti, persons who previously were infected with the Ogawa serotype of V. cholerae might be relatively more susceptible to reinfection with the Inaba serotype than with the Ogawa serotype because there tends to be stronger serotype-specific protective immunity. Immunologically naïve persons are equally susceptible to both serotypes. Because the Inaba strain is also biotype El Tor, its ability to survive outside of a host is likely the same as that of the Ogawa strain.

The two World Health Organization prequalified vaccines provide protection against the Ogawa and Inaba serotypes. In addition, the cholera rapid diagnostic tests detect all O1 serogroup infections, including Ogawa and Inaba serotypes.

This serotype conversion illustrates the increasing diversity of V. cholerae in Haiti (2) and emphasizes the importance of continued public health surveillance by the National Public Health Laboratory and CDC, which are partnering to establish a laboratory-enhanced sentinel surveillance system for a range of infectious diseases, including cholera and other diarrheal diseases. The system will provide data to determine the burden of diarrheal disease attributable to cholera and to help direct prevention efforts and programs to reduce morbidity and mortality from cholera in Haiti.

Reported by

National Public Health Laboratory; Ministry of Public Health and Population, Haiti. CDC Haiti Office; Health Systems Reconstruction Office, Div of Foodborne, Waterborne and Environmental Diseases, CDC. Corresponding contributors: Joan M. Brunkard, PhD, jbrunkard@cdc.gov, 404-718-4892; Deborah F. Talkington, PhD, dtalkington@cdc.gov, 404-639-3918.

References

  1. Ministry of Public Health and Population, Haiti. Rapports journaliers du MSPP sur l'évolution du choléra en Haiti. Port-au-Prince, Haiti: Ministry of Public Health and Population, Haiti; 2012. Available at http://www.mspp.gouv.ht/site/index.php. Accessed April 25, 2012.
  2. Talkington D, Bopp C, Tarr C, et al. Characterization of toxigenic Vibrio cholerae from Haiti, 2010–2011. Emerg Infect Dis 2011;17:2122–9.
  3. CDC. Defeating cholera: clinical presentation and management for Haiti cholera outbreak. Available at http://www.cdc.gov/haiticholera/clinicalmanagement. Accessed April 27, 2012.
  4. Longini I, Yunus M, Zaman K, Siddique AK, Sack RB, Nizam A. Epidemic and endemic cholera trends over a 33-year period in Bangladesh. J Infect Dis 2002;186:246–51.
  5. Ali M, Emch M, Park JK, Yunus M, Clemens J. Natural cholera infection-derived immunity in an endemic setting. J Infect Dis 2011;204:912–8.

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