An epidemiological investigation of a cholera outbreak in peri-urban slum settlements of Gujarat, India

Abstract

Background:

Cholera is an acute diarrhoeal disease caused by consuming contaminated food and water. The burden may remain underreported due to several issues like the low capacity of epidemiological surveillance systems, laboratory testing facilities, and socioeconomic disparities in urban slums. The disease has very short incubation period resulted in quick clustering of cases.

Aim:

A thorough outbreak investigation was carried out with the objective of strengthening the surveillance activity, finding out the sources of infection, and recommending necessary actions to control the outbreak immediately.

Methods:

An unusual increase in cases of diarrhoea was reported in slum area of Kalol town during the first week of July 2021. The stool samples were taken and investigated for confirmation and declaration of the outbreak by the Rapid Response Team. Time, place, and person distribution were carried out to generate a hypothesis and provide an immediate public health response to contain the outbreak. This study was conducted during the emergency public health response, no ethical approval was sought before the survey.

Results:

The cholera outbreak was confirmed when three out of five stool samples were positive for the bacterium V. cholerae O1 biotype El Tor serotype Ogawa. The overall attack rate and case fatality rate were 3.6% and 1.1%, respectively. The leakages caused the mixing of drainage water with the drinking water supply, which could be the possible cause of outbreak.

Conclusion:

The early identification and management of the cases, source reduction, health education on water chlorination, and hand hygiene were initiated based on our recommendations, which controlled the present outbreak.

Introduction

Cholera is an acute diarrhoeal disease caused by consuming contaminated food and water. While clean drinking water and good sanitation systems have been responsible for eradicating cholera in Europe and North America for decades, the disease continues to affect at least 47 countries worldwide, resulting in an estimated 2.9 million cases and 95,000 deaths per year.[1] However, cholera continues to be a significant public health problem and afflict millions of people in less developed countries where improved water and sanitation infrastructure are not widely available in many developing countries, including India. According to the World Health Organization (WHO), in 2019, 923 037 cases and 1911 deaths were notified from 31 countries.[2] Due to limitations in monitoring methods, many instances are not recorded, resulting in a mismatch between these numbers and the estimated disease burden. It might be due to several problematic issues, including the low capacity of epidemiological surveillance systems, laboratory testing facilities, and socioeconomic disparities in urban slums.[3,4]

The illness is typically spread via feces-tainted water or food, and since the incubation period is so brief (2 hours to 5 days), the number of cases may quickly multiply, resulting in a large number of fatalities.[5] In India, cholera epidemics are relatively frequent, underrecognized problems, and often remain underreported. Community-based surveillance of diarrhoea in an endemic area of Kolkata, India, has shown a cholera incidence of as high as 2.2 cases per 1000 person-years.[6]

More than half of the slums in India are not officially recognized by authorities, and the peri-urban slums and urban slums are at typical risk due to rapid urbanization.[7] On July 5, 2021, the state health department’s integrated disease surveillance program (IDSP) received ADD cases report from the informal settlement of urban primary health centers of Kalol block, Gandhinagar, Gujarat. On the same day, an investigation team was formed immediately. A thorough outbreak investigation was carried out with the sole objective of strengthening the surveillance activity, finding out the source of infection, and recommending necessary actions to control the outbreak immediately.

Material and Methods

Study setting

An unusual increase in the cases of diarrhoea was reported in Kalol town during the first week of July 2021. The Kalol is a municipality situated in Gandhinagar district of Gujarat state. The affected areas are predominantly urban slums having population of 11911.

Descriptive epidemiological investigation

After receiving information about an outbreak of acute gastroenteritis by the surveillance team, a rapid response team (RRT) from the State, including state epidemiologists, chief district health officer, experts from medical college, and chief officer of the town planning unit, visited the affected area on July 5 2021. A case of Acute Diarrhoeal Disease (ADD) was defined as the occurrence of three or more loose, watery stools (with or without vomiting) in the past 24 hours among town residents.[8] The team reviewed the integrated disease surveillance project (IDSP) annual financial year 2020-21 to confirm the suspected outbreak. The stool samples were taken and investigated for the confirmation and declaration of the outbreak. Descriptive analysis was carried out by reviewing the daily reports submitted by the local health team. Information regarding age, sex, place of residence, date of onset and days of hospital admission, treatment, and laboratory finding was collected. Time, place and person distribution were carried out to generate a hypothesis and provide an immediate public health response to contain the outbreak. Affected areas and populations under risk were identified based on the collected information. Specific recommendations were given throughout the outbreak for rapid containment.

Environmental investigation

In initial phase, the transect walks were carried out for environmental and sanitary investigations in the affected area. During the transect walk, water quality, water supply sources, and information about drainage systems were collected by observing and interviewing the local community and the water supply department. Total of five random water samples were taken from the water source, i.e., overhead tank, underground pipes, and households, on July 5 2021.

Laboratory investigation

An cholera outbreak is confirmed when V. cholerae O1 or O139 is isolated from a culture of the stool sample of the suspected cases.[9] The RRT collected five stool samples of the suspected cholera cases to confirm the outbreak. The samples were selected randomly from the patients who had complained of acute episodes of diarrhoea and were admitted to the local community health center. Stool samples were inoculated in alkaline peptone water. Standard bacteriological techniques tested the stool samples.[10] Anti-microbiological susceptibility of isolated pathological organisms was done by disc diffusion technique.

Ethical consideration

This study was conducted during the emergency public health response to the cholera outbreak and was designed to provide information to orientate the public health response. Therefore, ethical approval was not sought before the survey, and it was undertaken as a public health response to outbreaks rather than research.[11] Privacy, confidentiality, and rights of patients were ensured during and after the conduction of the study. Oral informed consent was obtained in each visited household after a detailed description of the existence of an outbreak, the objective of the study, and the planned use of the information. The investigation was aimed at achieving public good (beneficence) and collective welfare (solidarity); no harm was done to any individual (nonmaleficence); fair, honest, and transparent (accountability and transparency); and participants’ data were de-identified before analysis (confidentiality). Moreover, health education was carried out in each household regarding cholera transmission and prevention. The health education was primarily directed towards hand hygiene, chlorination, and cleanliness practices within households during outbreaks through trained medical teams.

Data reporting and analysis

The local health team recorded and reported deaths, infected patients, laboratory results of water samples, chlorination process to the affected areas, surveillance activity, open defecation practices, and other preventive measures based on the defined waterborne disease outbreaks response.[5] The data was collected and analyzed anonymously. The study was implemented in collaboration with the district health officials after obtaining authorization to carry out the survey.

Results

Outbreak detection, reporting

The local health authority of the Kalol town reported diarrhoea and vomiting to the district authority, as a total of 10 and 27 cases were detected on July 3, 2021 and July 4, 2021, respectively. The majority of the cases were reported from the five major areas, that is, Shreyas slum, Trikamnagar, J.P lathina Chhapra, Ratish slum, and Bhagatni Chali [Figure 1]. The affected areas were visited by RRT from State on July 5 2021.

Figure 1.

Location of the outbreak affected area on map

Outbreak confirmation and declaration

The suspected outbreak was confirmed after analyzing the annual IDSP reports of previous years of the local health centers. Water samples from both overhead tanks and three random samples from underground pipes, households were sent for the biological and culture testing to the Water and Sanitation Management Organisation (WASMO), Gandhinagar. The water samples were collected and transported on July 5, 2021. On the same day, five stool samples from the admitted patients were collected and sent to the microbiology department of Gujarat Medical Education and Research Society (GMERS) medical college for microbiological testing through a reverse cold chain. The cholera outbreak was confirmed when three out of five stool samples were positive for the bacterium V. cholerae O1 biotype El Tor serotype Ogawa.

Outbreak investigation and spread

The RRT traced the index case back to the household, where we found leakage in drainage pipes contaminating the drinking water supply. The index case was a 5.5-year male who presented with acute diarrhoea and vomiting on July 3, 2021 and was reported dead on July 5, 2021. The mean age of the reported cases was 30.9 (21.5 S.D.) years. Out of all 437 cases, 207 (47.4%) cases were belonged to the aged 16 to 47 years. The age distribution of the patients is as per Table 1. Nearly more than half (53.5%) of the patients were female. [Table 2] Almost half of the patients had vomiting with diarrhoea, while 25 (5.7%) patients had fever with diarrhoea. [Table 3] The overall attack rate of ADD was 3.6%, and the case fatality rate was 1.1%. The epidemic curve depicts that the first case occurred on July 3 2021. The curve gradually peaked on July 8, 2021, following which there was a gradual descent in the occurrence of new cases of diarrhoea. [Figure 2] The last case was detected on July 16, 2021. The place distribution was the recorded through geo-tagging of the cases according to address.

Table 1.

Age distribution of the patients (n=437)

Age-group	Frequency	Percentage
0-2 years	30	6.9%
3-5 years	42	9.6%
6-15 years	52	11.9%
16-45 years	207	47.4%
46-60 years	46	10.5%
>60 years	60	13.7%
Total	437	100.0%
Mean (in years)	30.9±21.5
Median (in years)	28

Table 2.

Sex distribution of the patients (n=437)

Sex	Frequency	Percentage
Male	203	46.5%
Female	234	53.5%
Total	437	100%

Table 3.

Profile of chief complaints (n=437)

Chief complaints	Frequency	Percentage
Diarrhoea only	193	44.2%
Diarrhoea and vomiting	219	50.1%
Diarrhoea, fever, and vomiting	25	5.7%
Grand Total	437	100%

Figure 2.

Epidemic curve and source reduction intervention

Source of infection

The most affected areas were slums, where morbidity and mortality had been observed. During the transect walk through the community, open defecation practices and improper hand hygiene practices were observed. The affected area was supplied by an overhead tank of 10 lakh liter capacity, which was then supplied through the underground pipes to the households of the affected areas. This water was being utilized for various purposes (washing clothes, cleaning, drinking, cooking, etc.) by residents of the affected areas. There were four leakages found in the affected area during the initial survey. The leakages caused the mixing of drainage water with the drinking water supply, which could be the possible cause of the outbreak. There was no history suggestive of food poisoning as there was no large gathering within the past one week of the symptoms.

Action taken

After confirmation of the suspected cholera outbreak, a total of 22 teams were deployed in the outbreak-affected area, including four medical officers and 44 paramedical staff. Additional human resources were deployed to cover the affected area. Early detection and prompt symptomatic treatment were initiated through intensified active surveillance. Daily average, 3440 households and a total of 14080 people were surveyed in the affected areas of the outbreaks. During the house-to-house survey, 290 close contacts were identified and treated accordingly.

The existing drinking water supply was closed temporarily for source reduction. Potable drinking water was supplied from nearby facilities using special water-carrying tankers in outbreak-affected areas. A total of 14217 oral rehydration therapy (ORS) packets and 81840 chlorine tablets were distributed in the affected area with demonstration of its use by front-line health workers. The bacteriological examination of the drinking water sample was also carried out and also it was tested for residual chlorine. The positivity rate for the chlorine test was observed to increase from a baseline of 26.7% to 72% at the outbreak’s end.

In the water distribution system, total of 12 leakages were identified in the affected geography and repaired during the first week of the outbreak, that is, July 7, 2021 to July 15, 2021. Super chlorination and overhead tank cleaning were carried out daily through intersectoral coordination with the water supply and town planning department.

Risk communication was carried out of use boiled water, ORS, proper handwashing, and the importance of chlorinated water in the affected area. A dedicated helpline number was made 24 hours available at Urban Primary Health Centers till the last case reported. Logistics were mapped and supplied to the health teams directed towards the hospitals and community surveys.

Discussion

With the resources we have now, every cholera mortality may be averted. Cholera transmission is a significant risk in areas with inadequate sanitation, restricted access to clean water, and poor hygiene habits. Cholera “hotspots” are defined as distinct and relatively small regions with the highest cholera burden, which play a critical role in cholera transmission.[5,12]

Sporadic cases of acute diarrhea disease are frequently reported in different parts of India throughout the year.[7] Cholera is one of the major infectious diseases with epidemic potentials which is common amongst slums setting with overcrowding, improper sanitary facilities, and inadequate personal hygiene.[7] The present outbreak mainly affected residents of urban slum areas, Kalol town, Gandhinagar district. The population in these areas shares the common source of water supply and practicing poor domestic and personal hygiene. In our investigation, we identified leakage in the water distribution system and found contaminated water at the house of the index case. Later on, three other leakages were found in the water distribution system. The leakage in water distribution pipes is a common phenomenon in India. Urban areas in developing countries receiving piped water systems are vulnerable to cholera outbreaks due to disrupted quality system maintenance of water distribution systems.[13] The leakages in water distribution led to the mixing of drainage water with the drinking water supply, which could cause the present outbreak. The prompt identification and repair of the leakage through intersectoral coordination prevented the propagated spread of the outbreak. Cholera outbreak in Delhi shown propagated spread due to delay in the leakage repairing.[14] In the present outbreak, it was also noted that the incidence of cases declined after superchlorination of tank, cleaning of the water source and tank, and distribution of safe drinking water through the portable water tank. The small- and large-scale chlorination of drinking water and repair of drinking water pipelines have been prioritized during cholera outbreaks in the past.[15,16,17,18]

The index case was of 5.5-year-old male children, and 16.5% of all cases had age five years or less in the present outbreak. The majority of the patients (47.4%) belonged to 16–45 years. Variation was reported in the age distribution of the affected patients in the different outbreaks. In an outbreak investigated in Gujarat by Koria et al.,[19] most of the affected patients (71.1%) belonged to the middle age group, that is, 21 to 40 years, while only 1.7% of patients had aged less than 10 years. Contrast age distribution was reported by Shah et al.,[16] in which the majority of the patients (44%) had aged less than 21 years. The male-to-female ratio in our study was 1:1.2, while in a study by Panda et al.,[20] it was 1:1.2, and Goswami et al.[21] showed 1.8:1, and Masthi et al.[22] showed a male-to-female ratio of 1:1.55. In the present outbreaks, 1.1% of the case fatality rate was reported. The case fatality rate was reported as less than 1% in various parts of India (overall 0.37%).[6] The underestimation of the numbers of the affected individual can be the reason behind the discrepancy in the fatality rate. In the present outbreak, the bacteriological examinations of the stools revealed V. cholerae O1 biotype El Tor serotype Ogawa as the causative agent organisms. Many other outbreaks in the different parts of India also reveal the same organism.[6,16,19,22] In the present outbreak, all the ADD cases of ADDs had received complete treatment at the primary and community health centers. Those who had mild dehydration were treated at home with ORS through the support of front-line health workers.

Recommendation

After the investigation, the RRT had provided the following recommendations to prevent future outbreaks:

1. Ensure close multisectoral coordination in case of acute diarrheal diseases outbreaks, eliminate the leakages in the case identified within affected areas.

2. Rigorous steps to avoid open field defecation under Swachch Bharat Abhiyan and ensure regular cleaning and chlorination of water storage tanks.

3. Prepare the resource mobilization plan for future cases and apply mock drills to prepare the staff to handle the sudden rise of the cases.

4. Train the front-line workers periodically on WASH practices and provide tools to disseminate the behavior change communication within the community with COVID-19 appropriate behavior.

5. Periodic awareness sessions will be planned with Mahila Aarogya Samiti’s support (MAS) under the National Urban Health Mission (NUHM).

6. Enhanced epidemiological and laboratory surveillance needs to identify the cholera hotspots areas across the countries.

A cholera outbreak was investigated in the slum areas of the Kalol town of Gandhinagar district. The RRT established that contaminated drinking water was the primary source of the present outbreak. The drinking water was contaminated due to cross-linkage between the drinking water line with the sewage line. Poor personal hygiene and overcrowding are also identified as risk factors in slum areas. The early identification and management of the cases, health education on chlorination of water and proper hand hygiene were initiated based on our recommendation, which controlled the present outbreak.

Conclusion

Acute diarrheal disease outbreaks are widespread in this specific geography. The State and district health authorities should identify these spots and devise multidimensional strategies involving all the government departments. The local customized plans should be developed across the State to establish the surveillance and response system to prevent such outbreaks. Implementing environmental targeted interventions such as the renovation of existing water storage facilities, monitoring the water and sewage lines, constructing standard sanitary latrines, and establishing appropriate waste disposal systems are sustainable long-term measures to prevent future outbreaks.

Financial support and sponsorship

District Health Departnment, Gandhinagar District and Department of Health and Family Welfare, Government of Gujarat, Gujarat.

Conflicts of interest

There are no conflicts of interest.