Cholera Outbreak, Laos, 2007

EID Journal Home > Volume 16, Number 4–April 2010

Volume 16, Number 4–April 2010
Letter
Cholera Outbreak, Laos, 2007
Noikaseumsy Sithivong, Hidemasa Izumiya, Khampheuy Munnalath, Traykhouane Phouthavane, Khampheng Chomlasak, Lay Sisavath, Arounnapha Vongdouangchanh, Phengta Vongprachanh, Haruo Watanabe, and Makoto Ohinishi
Author affiliations: National Center for Laboratory and Epidemiology, Vientiane, Laos (N. Sithivong, K. Munnalath, T. Phouthavane, K. Chomlasak, L. Sisavath, A. Vongdouangchanh, P. Vongprachanh); and National Institute of Infectious Diseases, Tokyo, Japan (H. Izumiya, H. Watanabe, M. Ohinishi)

Suggested citation for this article

To the Editor: Cholera is a major public health problem in countries where access to safe water and adequate sanitation cannot be guaranteed for all. Vibrio cholerae serogroups O1 and O139 are the causative agents of cholera (1). One of the most powerful virulence factors in this organism is cholera toxin encoded by the ctxAB gene, located on the CTX prophage. V. cholerae O1 is classified into 2 biotypes, classical and El Tor. The El Tor type of V. cholerae O1 is responsible for the ongoing seventh worldwide pandemic of cholera (2). The sequence of ctxB of a certain strain has been believed to correspond to its biotype; that is, a biotype classical strain has classical type ctxB, and a biotype El Tor strain has El Tor type ctxB. However, recent research studies suggest that novel types of V. cholerae O1, hybrid strains, and altered El Tor or El Tor variant strains (1,3) are emerging. Altered El Tor or El Tor variant strains are biotype El Tor but produce classical cholera toxin (3,4). Recent reports suggest that this type of V. cholerae O1 is spreading to many areas of the world (5).

In December 2007–January 2008, a cholera outbreak occurred in Xekong Province in southeastern Laos, in the Mekong Basin. The first case of the outbreak was detected on December 23, 2007. The outbreak spread to 10 villages and lasted through January 2008. Specifically, in the Thateng District, 117 cases occurred and 2 deaths were reported. The sources of the outbreak were suspected to be regularly used water. In October 2007, 2 months before the outbreak, 3 sporadic cases of V. cholerae infection had been identified in Vientiane (the capital city) and Xaignabouri Province in north-central and northwestern Laos, respectively. The outbreak investigation in the Xekong Province identified no linkage between these sporadic cases and the outbreak cases.

In this study, we analyzed 18 V. cholerae isolates obtained in 2007: 3 were from patients with sporadic cases, and 15 were from the Xekong outbreak (13 from patients and 2 from water samples). All the isolates were serotype O1 Ogawa and biotype El Tor, but their ctxB types were classical, according to the method previously described (6). This finding indicates that they were the type of altered El Tor.

Suggested Citation for this Article
Sithivong N, Izumiya H, Munnalath K, Phouthavane T, Chomlasak K, Sisavath L, et al. Cholera outbreak, Laos, 2007 [letter]. 2010 Apr [date cited]. Available from http://www.cdc.gov/EID/content/16/4/745.htm

DOI: 10.3201/eid1604.091493

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