Investigation of an Outbreak of Hepatitis A in a Coastal Area,Kerala,Southern India

Abstract

An outbreak investigation was initiated following an unusual occurrence of hepatitis A reported among people residing in the coastal belt of Vadi to Vedikunnu area, Kollam district, Kerala, southern India. The time frame of disease occurrence, pattern of its distribution, and the incubation period of hepatitis A infection indicated the probability of occurrence of the outbreak as a result of pipe line water contamination due to mixing of sewage from a canal. The results add evidence to the epidemiology of hepatitis A in the state and warrant the establishment of an efficient water quality surveillance system.

Viral hepatitis remains an important public health problem in India. Several large outbreaks of hepatitis A have been reported in the country during the past decade.^1-3 Kerala, the southernmost state, is undergoing an epidemiological transition from high endemicity to intermediate endemicity, and has experienced large number of outbreaks of hepatitis A in recent years.^3-6

On October 14, 2015, an unusual occurrence of 20 probable hepatitis A cases was reported to the District Surveillance Unit, Kollam from the coastal belt of Vadi to Vedikunnu area. ⁷ An outbreak investigation was initiated by the district health administration with the objective of describing the epidemiological features of the hepatitis outbreak and to make recommendations to further prevent the spread of the disease. The investigation team included physicians, epidemiologists, and multipurpose health workers.

Vadi to Vedikkunnu area is a coastal belt at Kollam district, stretching for about 2 km, with a total population of around 30 000. The area is marked with overcrowding, open but cemented drains and closely clustered houses. Majority of the residents depend on public water supply for drinking and other domestic activities. The area experienced an outbreak of hepatitis A during 2009 and the nearby areas reported many sporadic cases in 2014 and 2015.

We visited 15 cases initially to describe the clinical presentation of illness. We confirmed the diagnosis by testing blood samples at the State Public Health Laboratory. The comparison with the background data confirmed the existence of an outbreak of hepatitis A in the area. A probable case of hepatitis A was defined as an acute illness with fever or loss of appetite followed by yellowish discoloration of sclera or urine after September 1, 2015 in a resident of Vadi to Vedikunnu coastal area. Case definition was framed based on group consensus, and it has been made simple to pick up the cases from the community by the field-level health workers. A line list of cases was generated by visiting each and every house in the area over 2 days. Information regarding the date of onset, age, sex, place of residence, and treatment were collected. The catchment area hospitals and traditional healers were visited to get information regarding patients. Field-level and hospital-based surveillance was strengthened in the nearby areas.

Attack rates of acute hepatitis A by age and gender were calculated. An epidemic curve (Figure 1) was drawn and a spot map was generated with cases marked along with the water sources. Key informant interviews were conducted with 15 people who acquired the disease recently, local leaders, health workers in that area, local pump operators, and water authority officials. Information regarding the source of drinking water, drainage system, important events before the onset of illness, public gatherings, exposure to outside food, and local food vendors were collected. There were 3 water sources in the area: The first is the major water supply to the entire city from Sasthamcotta freshwater lake, second is a pump house located near the canal, which pumps water directly without overhead tank, and a third is near the collector’s bungalow where water is pumped to the overhead tank and directly supplied from there. There were provisions in the standard operating procedure for redistributing water supply from different sources in case of need. Sanitary inspection was done by visiting the pump houses and water lines. Log book for chlorination was verified to identify the frequency of chlorination and supply of public tap water. Six water samples were collected from different areas for microbiological analysis and residual chlorine.

Figure 1.

Epidemic curve showing number of cases of hepatitis A by week of onset, Kollam 2015.

Ninety-eight cases were on the line list with an attack rate of 0.33%. Attack rate among males was 0.0.38% (56/14525) and among females was 0.28% (42/14811). 24.5% of the affected cases were in the age group 26 to 35 years, while 3.2%, 21.4%, and 23.4% were in the age groups 6 to 15, 16 to 25, and 36 to 45 years, respectively. Epidemic curve suggests that it could be a common source outbreak with a sharp rise started from the third week of September, which peaked at the second and third week of October, followed by a rapid fall. No death or severe complications were reported. The geographical distribution of the cases suggested clustering of cases along with water supplied from second pump house. One of the water samples collected from water supplied from second pump house had grown Escherichia coli in pure culture indicative of contamination, while other samples did not show any growth.

There is a major canal that serves as a major waste dumping site, near the second pump house. We found out that an excavation using an excavator (JCB India Limited) for demolishing illegal housings near the banks of the canal happened on August 25. The houses that were demolished did not have an appropriate septic tank system and the canal served as the main drainage source for sewage. During the process of demolishing, the pipelines that were interlinked to each other got ruptured and gradually the pipes near the pump house in the bank of canal got clogged with mud and drainage. As a result, the water supply from the second pumping station had been stopped from September 15 to 24. During that time, water to these areas was pumped from other pumping station. After the maintenance work, pump house restarted functioning on September 25. Initial cases were reported during the last week of September and the cases continued to occur till October third week indicating the presence of a persisting source for 3 to 4 weeks.

The time frame of disease occurrence, pattern of its distribution and the incubation period of hepatitis A infection indicated the probability of occurrence of the outbreak as a result of pipe line water contamination over the entire area. The mixing of sewage from canal with water supply in pipeline due to disturbances in the system during the excavation process could have contributed to this outbreak. Peaks in the epidemic curve after initial falls could be either due to repeated exposure or due to person-to-person transmission or both.

About 60% of the households that reported cases did not have the habit of boiling drinking water.Residents reported absence of smell of chlorine in pipeline water for past few months. We could not find any other event or factors that could explain the current outbreak.

Presentation of hepatitis A is determined by the age of exposure, which tends to be asymptomatic or subclinical during childhood and symptomatic usually among older children adolescents and adults. ⁸ In Kerala, with a comparatively better sanitation and hygiene and a better standard of living, children often escape infection in early childhood. Ironically, these improved economic and sanitary conditions led to a higher susceptibility in older age groups. Presence of a previous outbreaks in the area, host-related immunity factors, and behavioral factors like boiling water could explain why others using the same water supply were not affected.

This investigation was helpful in documenting the missed opportunities for prevention of this outbreak. The investigation helped in convincing the water authority regarding their role in preventing outbreaks and the local self-government and administration regarding the importance of sanitary regulations and urban health workers about the need for proper surveillance. At least 2 major outbreaks of hepatitis A in the state have been due to the mixing of sewage with the drinking water supplied through piped water distribution.^4,5 The findings on persistence of source of infection even after 3 to 4 weeks following contamination of pipeline highlights the need to have an efficient water quality surveillance and the importance of sanitizing pipelines after contamination before using it again for flow of water.