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Indian Journal of Community Medicine

An Explosive Outbreak of Eltor Cholera Amongst Migrant labourers of a Brick Field Area Near Calcutta

Author(s): P.G. Sengupta, S.K. Mondal, Dipika Sur, P. Dutta, D.N. Gupta, S. Ghosh, T. Ramamurthy

Vol. 26, No. 3 (2001-07 - 2001-09)

Abstract :

Research question: Why did the localised diarrhoeal outbreak occur in two brick fields of Calcutta?

Objectives:1. To study the epidemiological features of the outbreak. 2. To assess and rationalise home management of cases. 3. To identify the causative agent(s) with antimicrobial susceptibility pattern.

Study design: Cross-sectional study.

Setting: Brick fields located in the south-western side of Calcutta municipal area and situated near the bank of river Hoogly.

Participants: 246 individuals including brick field labourers along with their family members.

Statistical analysis: Simple proportions.

Results: A localised outbreak of diarrhoeal diseases occurred between 4th and 18th April 2000, in which 71 persons suffered from acute watery diarrhoea and vomiting. The overall attack rate was 28.9%. Two out of 5 faecal samples collected from domiciliary diarrhoea cases, were positive for V. cholerae 01. There was extensive spread of V. cholerae in the surrounding aquatic environment. Of the 22 water samples collected from different sources, 10(45.4%) were positive for V. cholerae 01, which included tube well water, stored water and cesspool water. All the strains of V. cholerae 01 isolated from cases and water samples, were sensitive to tetracycline, norfloxacin, ciprofloxacin, gentamycin, chloramphenicol but resistant to furazolidone which is the recommended drug for children. The strains were also resistant to co-trimoxazole, nalidixic acid, streptomycin and ampicillin. Clinical, epidemiological and microbiological data, all pointed towards a localised and explosive outbreak of cholera caused by contamination of drinking water and the possible source of such contamination was a case, which occurred during first week of April.

Keywords: Explosive outbreak, Brick field, Investigation, Cholera, Furazolidone resistance


Cholera is one of the major infectious diseases with epidemic potentials especially among communities living in congested urban slums and vast rural areas without proper sanitary facilities, which are typical of endemic areas1,2. West Bengal, located in the delta of the Ganges has been recognised as the homeland of cholera since recorded history. Being endemic for cholera, localised outbreaks are not uncommon as have been reported from time to time3,4. Factors such as poor personal hygiene, contaminated water and lack of environmental sanitation have contributed in perpetuation of this organism for generations with occasional flare-ups in the form of epidemics.

We report here a localised outbreak of cholera due to V.cholerae 01 which occurred between 4th and 18th April 2000, amongst a group of migrant labourers and their families in a brick field area under the Calcutta Municipal Corporation.

Material and Methods:

The investigation was carried out on two consecutive days on 12th and 13th April, 2000.

Affected area:

A number of brick fields are located in the south-western side of Calcutta municipal area situated near the bank of river Hoogly. They are separated from the river bank by a strip of land about 50 yards in width. Each of the brick field, has a barrack which shelters the labourers along with their family members. During their stay in the brick field areas, each family is provided with a single room (approx. 10 x 8 ft) and a small verandah (corridor) for accommodation and cooking. For drinking water, there is a tubewell in each brick field with broken platform and surrounding stagnant water. Water for domestic use is stored in wide mouthed containers. The river water has been tunneled into the low lying excavated ditches adjacent to the brick fields for the purpose of preparation of bricks. The water flow from the river has been cut off after tunneling, by blocking the tunnel with mud resulting in cesspools of different sizes. These cesspools are utilized for bathing, washing or ablution purposes. There is no sanitary or other toilet facility and the people use open land around the brick fields for defaecation.

Collection of data:

A house to house survey using a standard proforma was carried out, to detect all cases and deaths due to diarrhoea using a two week recall. Sources of drinking and domestic water supply and storage of drinking and cooking water were noted. General cleanliness including personal and domestic hygiene, housing conditions and available living space was also ascertained. All detected diarrhoea cases were assessed and detailed clinical history and treatment received were recorded. Assessment and management of cases:

Diarrhoea cases detected during the survey were clinically assessed using standard WHO guidelines5. Appropriate management was immediately provided. Two local persons (unqualified allopaths) who were the treatment providers for the residents of the brick fields, were identified and interviewed to elicit case management procedure followed by them and they were also trained about rational home management of diarrhoea. They were made local depot holders for ORS and necessary logistic support was provided. Signs of dehydration in the detected cases were demonstrated to them and they were advised to refer severe dehydration cases to the hospital forthwith.

Laboratory procedures:

Stool samples were collected in Carry-Blair transport media from fresh domiciliary cases detected during the survey. Water samples were collected in 500 ml sterile bottles from various sources including tube wells, stored water from affected families and cesspools in the affected brick field area. Samples were processed for presence of Vibrios, E. coli, Shigella and Salmonella species using standard techniques6. Briefly, for selective isolation of Vibrio cholerae, two to three loopfuls of faecal samples were plated on thiosulphate-citrate-bile salt-surcose agar (TCBS; Eiken Chemical, Tokyo, Japan). After overnight incubation at 37 C, typical colonies were inoculated onto multitest medium to facilitate rapid presumptive identification of Vibrio cholerae. Reaction on the multitest medium was examined for oxidase reaction. About 100 ml of water samples collected from the different sources, were passed through sterile membrane filters (pore size 0.22*; Millipore, MA, USA) using a filtration manifold (Millipore). After filtration, membrane filters were directly introduced in tubes containing alkaline peptone water (APW; pH 8.0) and incubated for 6-8 hrs. at 37 C. Enriched culture in APW was processed for the isolation of Vibrio cholerae as described above. One ml aliquot of enriched culture was processed for the detection of cholera toxin. A subunit gene (ctx A) and biotype EIT or specific orfB region by a multiplex polymerase chain reaction (PCR) assay using the methods described above7. Antimicrobial susceptibility testing was done by the modified Kirby-Bauer disc diffusion technique8.

Results and Discussion:

The outbreak was confined within two adjacent brick fields. Work in the brick fields usually starts when the rainy season is over each year, i.e. around October, before the winter sets in. The work continues till around end of April after which the labourers move away from these temporary settlements to their original home place, which is mostly in the state of Bihar. It was obvious that the available space of 80 sq.ft. provided to each family, was not sufficient even for a single person and, therefore, there was overcrowding for a family with one or two children, when the recommended floor space per person is 100 sq.ft.9. In the absence of continuous piped water supply, the families were found to store water for drinking and domestic purposes in wide mouthed containers without cover, which facilitated contamination of stored water by infected hands.

The distribution of cases was as that seen in a common source outbreak. The cases started occurring from 4th April 2000 and the maximum number of cases were noted on 11th April, declining slowly thereafter.

Most of the cases presented with profuse watery diarrhoea and vomiting and 24(33.8%) of them were admitted to the Infectious Diseases Hospital, Calcutta. The first case was a female child aged 4 years who had onset with profuse watery diarrhoea and vomiting and had to be hospitalised, the single death which occurred after hospitalisation was that of a 7 year old male child who was admitted with severe dehydration and profound shock on 5th April and died on the same day. The local treatment providers were prescribing several antibiotics in combination with antiperistaltics for the domiciliary cases. Some were also prescribed oral rehydration salts with inadequate and faulty instructions for preparation and administration.

Table I: Age distribution of the diarrhoea cases with attach rates.

Age group No. of cases Population
at risk
rate (%)
(in years) Domiciliary Hospitalised Total
0-4 11 7 18 41 43.9
5-9 07 3 10 39 25.6
10-14 06 3 9 29 31.0
15-44 20 2 29 116 25.0
45+ 3 2 05 21 23.8
Total 47 24 71 246 28.9

Table I shows the age distribution of the cases with the attack rates. Of the 246 population at risk, living in 54 families, 71 cases of acute watery diarrhoea occurred giving an overall attack rate of 28.9%. Highest attack rate (43.9%) was noted amongst children below 5 years of age. However, no age group was spared. The ratio of hospitalised to domiciliary cases was 1:2.

Two out of 5 stool samples (40%) collected from domiciliary diarrhoea cases, were positive for V.cholerae 01. A total of 22 water samples were collected from different sources, including 2 samples from tube wells, 12 from stored water and 8 from cesspool water. Of these, 10(45.4%) were positive for V.cholerae 01. One of the samples collected from tube well was positive for V.cholerae 01. Five (41.7%) out of 12 stored water samples were also positive for the same pathogen. The remaining 4 positive water samples were collected from 8 cesspools indicating extensive spread of V.cholerae in the surrounding water sources. All V.cholerae strains were biotype elTor and serotype Ogawa. All the strains were uniformly sensitive to tetracycline, norfloxacin, ciprofloxacin, gentamycin and chloramphenicol but resistant to furazolidone, co-trimoxazole, nalidixic acid, streptomycin and ampicillin. Resistance to furazolidone, which is the recommended drug in management of paediatric cholera cases, is a matter of concern as tetracycline is contraindicated for this age group.


Clinical, epidemiological and microbiological data, definitely revealed that the present localised outbreak was of cholera. Every year groups of migrant labourers with their families come to these brick fields for work during the period from winter till the end of summer. Records of local health authorities indicated that watery diarrhoea cases with occasional death have occurred practically every year amongst this labourer population. During the present outbreak, higher attack rate in children below five years of age clearly indicated that the area is endemic for cholera and the outbreak was an explosive one amongst an endemic migrant labourer community.

Cholera is known to be transmitted by faeco-oral route, mainly through contaminated water or food10. It appears from the explosive nature of this outbreak and evident from the epidemic curve, that the most probable cause was contamination of drinking water source. In addition indiscriminate defaecation and low levels of personal and domestic hygiene led to extensive environmental contamination, which helped perpetuation of this infection amongst the migrant labourers almost for a period of three weeks.


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P.G. Sengupta, S.K. Mondal, Dipika Sur, P. Dutta, D.N. Gupta, S. Ghosh, T. Ramamurthy

National Institute of Cholera and Enteric Diseases, Calcutta

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