Volume 26-19
1 October 2000

[Table of Contents]

HEPATITIS A IN THE NORTHERN INTERIOR OF BRITISH COLUMBIA: AN OUTBREAK AMONG MEMBERS OF A FIRST NATIONS COMMUNITY

Introduction

In August 1999, the British Columbia Centre for Disease Control Society (BCCDCS) was notified of an outbreak of hepatitis A in the Northern Interior Health Region. By 31 August 1999, 14 cases had been reported in the Northern Interior, compared to two cases in 1998 and three cases in 1997. Cases related to the outbreak had also occurred on a First Nations reserve in the neighboring North West Health Region. To prevent further cases, the BCCDCS along with the local and federal health authorities initiated an in-depth investigation of the identified cases. This article describes the outbreak and the resulting public-health response which included active immunization of populations identified to be at risk through epidemiologic links and/or salivary antibody testing.

Outbreak Description

Between April and September of 1999, 23 confirmed outbreak related cases of hepatitis A were reported to the BCCDCS (Figure 1). A confirmed case was defined as any person who was seropositive for anti-HAV IgM, with or without symptoms of hepatitis A.

Figure 1 Hepatitis A cases in the Northern Interior of British Columbia, April-September, 1999, by week of onset

Eighteen of the cases (78%) were members of a First Nations band in Northern British Columbia. Of the eighteen cases, two were permanent residents on the reserve and the remainder listed Prince George as their primary place of residence. All cases were eventually linked to the six initial cases. There were no cases related to foreign travel or contaminated water supplies. The majority of the cases (20) resided within the Northern Interior Health Region, two cases lived within the North West Health Region, and one case was a resident of the Cariboo Health Region.

Nine (39%) of the cases were females and 14 (61%) were males. The ages ranged from 1 to 32 years with a median of 11 years. Children between 1 and 14 years of age accounted for 57% of the cases. The remainder of cases (43%) were between the ages of 25 and 32 years. There were no cases between the ages of 15 and 24, or > 32 years of age. However, one probable case, aged 38 years, declined testing.

The investigation revealed that the six initial cases comprised one First Nations family whose members were all infected around the same time. The onset of symptoms for the first six cases occurred between April 30 and May 4, 1999. The index family included five males and one female ranging from 3 to 27 years of age (index cases). Two additional family members were given ISG and did not become infected. The source of the infection of the index family was investigated but never identified. The remaining 12 cases involving First Nations people can be linked to other cases through familial and social contacts.

Of the five non-Aboriginal cases, one was a classmate of an index case, and two were believed to have resulted from food-borne transmission. The latter two individuals frequented an establishment where a known case worked as an occasional food-handler. These individuals can be linked to the remaining two cases by familial and social contacts. Notably, the final case reported that his high risk contact consisted of sharing food and cigarettes with an identified case.

Outbreak Response

The public-health response to the outbreak was coordinated between the BCCDCS and the public-health authorities for the First Nations reserve and the Northern Interior, the North West, and the Cariboo Health Regions. Public-health nurses (PHNs) in each of the units administered surveillance forms and collected demographic data on the cases including date of onset of symptoms, travel history, food-handler status, contacts, and laboratory results. PHNs initiated contact tracing, gave ISG to the close contacts, and performed continuing enhanced surveillance. Environmental investigation assessing food handling practices, water quality, and living conditions were conducted by the regional environmental health officers. Because the outbreak involved a complex network of social interactions and spanned a period of 5 months, from late April until late September, intervention was necessary at several points as the outbreak evolved.

ISG was routinely given to all close contacts. Four weeks after the first cases were reported, a 7-year-old female (Case 7) developed symptoms of hepatitis A and subsequently tested positive for anti-HAV IgM. The new case was a classmate of a member of the index family in a combination kindergarten/grade 1 class. The classmates of the two children were all given hepatitis A vaccine because of the likelihood of transmission among the children. No further cases involving the class occurred.

At about the same time, a second cluster of cases (Family B) was identified. A member of this family had attended several barbecues with the index family (Family A) in the spring. A 29 year-old female (Case 8) was identified as food handler working for a catering company. The case was excluded from food-handling work and her co-workers were given ISG. Regional public-health authorities investigated the catering company; hygiene practices were found to be satisfactory. Attendees of events catered by Case 8 during her incubation period were determined not to be at significant risk and extensive tracing was not undertaken. No cases involving the catering company were reported.

Comprehensive contact tracing for the index family at the beginning of the outbreak proved difficult. Consequently, one group of close contacts (Family C) was not discovered until August and the outbreak continued. Serologic testing confirmed that Family C linked the rest of the cases with the index Family A.

In late August another case, a 25 year-old female (Case 11), was identified as an occasional food handler at a local bingo hall. Two subsequent cases (Cases 12 and 13) were identified as patrons of the bingo hall. Regional public-health authorities investigated the bingo hall and rigorously evaluated the hygiene practices of the food handler. Case 11's food handling and hygiene were found to be adequate. Because she was already past the infectious period at the time of reporting, Case 11 was not excluded from work. Based on the environmental health officer's evaluation, tracing of bingo hall patrons was determined not to be necessary. No further cases related to the bingo hall were reported.

At the end of August, two cases (Cases 16 and 17) were reported on a First Nations reserve. A few weeks prior, a large potlatch/funeral had taken place on the reserve. The cases had participated in a day camp and an overnight church camp also attended by children from neighboring reserves.

Concern for the risk of large-scale spread of hepatitis A led to a vaccination campaign of the reserve population < 30 years of age. This intervention was a joint decision of the First Nations reserve, regional public-health authorities, and the BCCDCS in consultation with the Medical Services Branch, Health Canada. An immunization cut-off age of 30 years was adopted based on observations of a 1995 HAV outbreak on another First Nations reserve where almost all band members > 30 years of age were shown to be immune due to prior infection. In order to verify that appropriate age groups were being immunized, a sialoprevalence (salivary antibody) survey of HAV immunity was conducted concurrently with the vaccination program. Although the desired number of study subjects was not achieved, the survey demonstrated that - among on-reserve participants - 83% of those aged >= 25 years of age had salivary antibodies to HAV; beyond age 40, no susceptible individuals were discovered. No one < 15 years of age had demonstrable antibodies (Table 1). Data on sialoprevalence may be used to guide future hepatitis A vaccination programs.

Table 1 Frequency of anti-HAV IgM by age group

Discussion

For the past decade, reported rates for hepatitis A in British Columbia have exceeded the national average⁽¹⁾. In 1998, 386 cases were reported in the province for a rate of 9.65 cases per 100,000. In the past 2 years, men who have sex with men (MSM) and injection drug users (IDU) have been identified as primary risk factors: an outbreak of hepatitis A occurred in the Vancouver MSM population from 1997 to 1998⁽¹⁾. In past years, cases involving Aboriginal populations have contributed significantly to provincial statistics. A 1995 central Vancouver Island outbreak involving a First Nations community accounted for 14% of the provincial cases that year⁽¹⁾. While the absolute numbers of the most recent outbreak are not that large, the number of cases of hepatitis A reported in this outbreak represents an almost 10-fold increase from the previous year. None of the cases reported during this outbreak could be related to foreign travel. (One travel-related case of hepatitis A was reported to the Northern Interior Health Region earlier in the year.)

The distribution of this outbreak indicates propagation by person-to-person spread. The lack of a sudden, dramatic increase in cases made a point source unlikely. No common environmental source was identified. Although it was never determined how the index cases contracted the disease, our investigation satisfactorily established the chain of events and contacts by which the outbreak spread. Two cases appear to have been food-borne and were related to a bingo hall where a known case worked as an occasional food handler. No further cases related to the bingo hall were reported.

Previous analyses of hepatitis A outbreaks in Aboriginal communities have identified inadequate water supplies and high housing density on reserves as risk factors for outbreak propagation (Medical Services Branch, Health Canada: unpublished data, 1996). The First Nations reserve involved in this outbreak had satisfactory community drinking water and sanitary sewage systems. Household density may have been a contributing factor. Household density was often increased by house guests who, in turn, propagated the outbreak. The complex network of extended families and friends combined with the frequency and expanse traveled by First Nations families facilitated the spread of hepatitis A across a wide geographic area. These factors also made the outbreak investigation much more difficult.

Over half of the cases in this outbreak occurred in children < 14 years of age. Clinically, children are less likely to be symptomatic than adults and may shed viruses for extended periods of time. Poor hygiene and play activities may contribute to an increased risk of transmission between children.

The decision to immunize the population of the reserve with hepatitis A vaccine was made before the conclusions of the investigation were known. Two weeks prior to the appearance of the on-reserve cases, the reserve had been the site of a large and widely attended potlatch/funeral for a prominent band elder. Local and provincial health authorities had not yet determined whether food-borne transmission had occurred and there was concern that unknown cases may have participated in the potlatch food preparation. Subsequently, the investigation established that the cases of hepatitis A on the reserve involved only children and that no children participated in the potlatch. Immunization may have prevented further person-to-person transmission within the community. Clear guidelines for the use of hepatitis A vaccine in outbreak settings are required to ensure appropriate use of immunization.

Acknowledgments

The authors would like to thank all of those who participated in the outbreak investigation, especially the medical health officers, environmental health officers and PHNs of the Northern Interior and the North West Health Regions.

References

1. British Columbia Centre for Disease Control Society. Annual summary of reportable diseases. Vancouver, B.C.: Epidemiology Services 1998.

Source: J Harb, MSc, BA, CPHI(C), BCCDCS Field Epidemiologist, Field Epidemiology Training Program, Centre for Surveillance Coordination, Health Canada, Vancouver, B.C.; M Lem, MD, Community Medicine Resident, University of British Columbia, M Fyfe, MD, MSc, Associate Director, D Patrick, Director, Communicable Disease Epidemiology Services, BCCDCS, J Ochnio, PhD, S Dobson, MD, Vaccine Evaluation Centre, Vancouver, B.C.; J Hockin, MD, Director, Field Epidemiology Training Program, Health Canada, Ottawa, Ont.

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