Epidemiology and transmission of V. cholerae O1 and V. cholerae O139 infections in Delhi in 1993.

In 1993, rectal swabs from clinically suspected cases of cholera admitted to the Infectious Diseases Hospital (IDH), Delhi were examined for Vibrio cholerae Ol and 0139. Epidemiological data of 396 cholera cases were collected before the patients' discharge from IDH. Of the 1528 laboratory-confirmed cholera cases, 46% and 54% were caused by serotype Ol and 0139 respectively. Both serotypes appeared and disappeared simultaneously, and peaked during the same time of the year. However, the two serotypes affected persons of different age groups; about 65% of the Ol cases occurred in children aged less than 10 years, whereas this age group accounted for 40% of the cases due to V. cholerae 0139. Although there were some focal outbreaks due to serotype 0139, both serotypes had almost similar geographical distributions. Important risk factors for transmission of cholera were almost equally prevalent in the majority of both types of cholera cases. Since the seasonality, geographical distribution, and risk factors for transmission were similar for both serotypes, the study Indicates that the preventive and control measures are also likely to be similar. The study also shows that the emergence of V. cholerae 0139 in 1993 did not affect the incidence, seasonality, and epidemiology of endemic V. cholerae Ol El Tor strains in Delhi. Key words'. Cholera; Vibrio cholerae; Epidemiology; Disease transmission INTRODUCTION MATERIAL AND METHODS Vibrio cholerae 01 biotype El Tor entered India for the To monitor the trends on the incidence and seasonality first time in 1964 and Delhi in 1965. Thereafter the and the epidemiology of V. cholerae 01 biotype El Tor in disease became endemic (1). Epidemiology of cholera Delhi, a laboratory-based surveillance has been took a dramatic turn during the last months of 1992 when established since 1965-66. (7,8). As a part of the system, V. cholerae non-01, which was so far considered to have clinically suspected cases of cholera are referred to the no epidemic potential, became a major cause of epidemics Infectious Diseases Hospital (IDH), Delhi. All of them are in India, Bangladesh, and other countries (2-7). This offered stool examination (rectal swab) for isolation of V. strain was designated as V. cholerae 0139, another agent cholerae by standard microbiological techniques. Rectal of cholera. It emerged in Delhi in April 1993. swabs are collected (one each) in Venkatraman How the two serotypes of V. cholerae, El Tor and R^makrishnan fluid (VR) and i„ Cary-Blair medium, and 0139, behaved in Delhi during 1993, and whether the *ansPorted th*.laborato"^ tbe National Institute of emergence of V. cholerae 0139 altered the epidemiology Communicable Diseases (N CD), Delhi, which are about of endemic El Tor cholera are discussed in this article. ? ^ ^ fr0,m IDH' J" ^olerae isolates are identified by biochemical tests and confirmed by serology. In 1993, ——— all the isolates of V. cholerae non-01 were tested against Correspondence and reprint requests should be addressed to: antisera for V cholerae 0139 Dr. Jagvir Singh This content downloaded from 207.46.13.76 on Fri, 09 Sep 2016 04:43:56 UTC All use subject to http://about.jstor.org/terms Epidemiology of cholera In addition to the data generated by the surveillance system, we collected information on 702 cases of acute diarrhoea admitted in IDH by interviewing them before discharge. For this purpose, two surveyors visited IDH 2 to 3 times a week during June-September 1993. Data were collected about the patients' age, sex, clinical symptoms, occupation, and education. Data pertaining to the family were also collected regarding the sources of drinking water, water storage practices, type of latrine used, and hand-washing practices after defecation and before meals. The results of rectal swabs were not available when the epidemiological data were being collected. When the results from NICD became available, the data were analyzed for both types of cholera (V. cholerae 01 and 0139) separately. Of the 702 patients interviewed, 218 had V. cholerae 01 infection and 178 had V. cholerae 0139. For this analysis, we used the Epi Info software, version 5.01. To monitor the quality of water, NICD also collected As showj} m T^|e n, copiera cases due fg gjfftgf water samples from many areas with cholera cases, A serotypes had aimest sifpilaf ggpgrgpfoicg} §ppth and RohiPI ?ones were tjjg worsf (near or from the homes of patients) during the 1993 affected areas. Although not shown hepe, the fpajopity gf cholera season. These samples were examined for botb types occurred in pgsetflemegf gfid J.J. (slum) coliform count and faecal Escherichia co i. No attempt Monies. A few focal outbreaks due to y. ©13$ was made to isolate V. cholerae from the samples. A Were apparentFop exargpje an outbreak gf acute sample was labelled satisfactory based on the criteria laid it} § J (population down by WHO (coliform count <4 and faecal coll zero Zone) between i3 ^ j^p/lOOS; 196 cases'rife one per 100 mL water) (9). It may be mentioned that there death occurred About 3Q patients were admitted IDJ4, was a bias m the collection of water samples. Those water of which 15 wer£ itiye for y chol 0139. ' samples which were suspected to be contaminated were 'F more likely to be collected. Since V. cholerae Ol biotype classical no longer exists in India, V. cholerae Ol biotype El Tor will be mentioned as V. cholerae Ol in this article. Table I. Proportion of cholera 0139 in Delhi, 1993 cases by V. cftqlerae Ol ggpj Month Total no. of cholera cases Proportion of 01 V. cholerae Proportion ql QJI9 V. cholerae January-March 0 0 ' 0 April 81 9.9 90.} May 445 34.8 65,2 June 318 36.8 63.2 July 274 48.5 51,5 August 190 57.4 4?,6 September 144 74.3 m October 65 89.2 10-8 November 11 90.9 91 December 0 0 0 Total lias 45-6 54:4