Descriptive Analysis of Endemic and Travel Hepatitis - A cases in Ontario, 1998 to 2004

15 December 2006 Volume 32 Number 24

[Table of Contents] [Next]

TW Leung, BHSc, MHSc (1), L Vrbova, HonBSc, MSc (2)

1. Public Health Agency of Canada, Ottawa, Ontario

2. Ontario Ministry of Health and Long-Term Care, Toronto, Ontario

Introduction

The hepatitis A virus (HAV) is a highly resilient virus capable of surviving on human hands and inanimate objects.¹ The virus is most commonly transmitted by the fecal-oral route through person-to-person contact or indirectly via contaminated food and water². The clinical manifestations of HAV include jaundice, fever, malaise and in some cases, even fulminant hepatitis²; clinical severity of the illness increases with age³. Although most cases do not experience lifelong consequences, this acute infection remains a significant source of morbidity.

Groups at high risk for HAV include travelers to countries where HAV is endemic, men having sex with men (MSM) and intravenous drug users⁴. A recent survey of provinces and territories in Canada identified travellers as the highest risk group⁴. The purpose of this report is to describe and compare the epidemiology of endemic and travel-related HAV cases reported in Ontario from 1998 to 2004.

Methods

HAV is a reportable disease in Ontario under the Health Protection and Promotion Act⁵. During the study period, health units in Ontario reported all cases of HAV to the Ontario Ministry of Health and Long-Term Care using the Reportable Diseases Information System (RDIS). In 2005, health units began reporting in the Integrated Public Health Information System (iPHIS). All cases of HAV with reported episode dates between 1^st January, 1998 and 31^st December, 2004 were included. The case definition for HAV for this period was (a) clinically compatible signs and symptoms with demonstration of IgM anti-HAV or epidemiologic link to one or more laboratory confirmed cases of HAV and (b) an asymptomatic individual with anti-HAV IgM.

For this analysis, all reported cases were classified as either “endemic” or “travel” cases. Infections acquired in Ontario were considered “endemic” cases. Cases were classified as “travel” if the reported risk factor for acquiring HAV included travel or having lived outside of Ontario. Clinical characteristics of endemic and travel cases were analyzed together assuming that diagnosis and prognosis of HAV is similar, regardless of where the infection was acquired. Age-specific rates were calculated using 2001 Census population from Statistics Canada. Results were analyzed using SPSS Version 13.0. Mapping was done using Environmental Systems Research Institute Inc (ESRI) ArcGIS 9.0.

Results

During the period from January 1998 to December 2004, a total of 1,381 cases of HAV were reported. Of all reported cases, 57% (787/1,381) were endemic and 43% (594/1,381) were travel cases. The mean number of cases reported each year in Ontario was 197 (range: 144 to 318). The annual mean number of endemic cases was 112.4 (range: 72 to 222) compared to travel cases with an annual mean of 84.9 (range: 68 to 96). Figure 1 shows the annual number of cases and incidence rates during the study period.

The numbers of endemic and travel cases by onset month are shown in Figure 2 (cumulative) and in Figure 3 (time-series). The lowest number of endemic cases was in February. The highest number of travel cases was in April and September. Twenty-six percent of cases (356/1,381) were missing a date of onset.

Figure 1. Number and incidence of reported hepatitis A cases in Ontario by year reported, 1998 to 2004 (n = 1,381)

Figure 2. Number of endemic and travel hepatitis A cases in Ontario by onset month, 1998 to 2004 (n = 1,025)

Figure 3. Time-series of the number of endemic and travel hepatitis A cases in Ontario by epidemiological date, 1998 to 2004 (n = 1,381)

click on the image to enlarge

Figure 4 shows a map of incidence rates for endemic cases by health unit over the 7-year study period. Twelve health units had rates greater than 1.0 per 100,000 population. The highest rate was found in Renfrew County at 2.85 per 100,000 population.

Figure 4. Hepatitis A in Ontario by Health Unit, 1998 to 2004 (n = 787)

click on the image to enlarge

Demographics

Overall, 57% (793/1,380) of the cases were male. This overall sex distribution was similar between endemic and travel cases. Among endemic cases, the mean annual incidence of HAV was highest among males aged 20 to 29 (1.4 per 100,000 population) and 30 to 39 (1.6 per 100,000 population) (Figure 5). Among female cases, the highest mean annual incidence was in the age group 70 to 79 (1.1 per 100,000 population). The mean annual incidence rates for travel cases decreased with increasing age in both males and females (Figure 6). Male rates were higher than female rates for most age groups. The highest rates for both male and female were among children aged 0 to 9 years of age (1.7 per 100,000 population and 1.4 per 100,000 population, respectively).

Figure 5. Age and sex-specific mean annual incidence of endemic hepatitis A cases in Ontario, 1998 to 2004 (n = 1,377)

Clinical Characteristics

Of the 975 cases that reported at least one symptom, the following symptoms were most commonly cited: jaundice 41% (396/975), fever 34% (334/975), nausea and/or vomiting 25% (248/975) and abdominal pain 24% (231/975). (Percentages do not add up to 100%, since cases could report more than one symptom.)

More than half (58%) of the reported cases had no data on hospitalization. Among those cases for which hospitalization data was available, 69% of cases (405/587) had no history of hospitalization associated with HAV. Almost 26% (152/587) of cases reporting hospitalization status received inpatient care and 4% (21/587) received outpatient care. There were a total of six deaths during the study period, all of which occurred among endemic cases. HAV was listed as the cause of death for only two of the six cases, the cause being unknown for the other four. The death rate therefore may range from 0.1% (2/1,381) and 0.4% (6/1,381). The mean age at death was 63 years of age (median: 75 years).

Figure 6. Rates of travel hepatitis A cases in Ontario by age group, 1998 to 2004 (n = 1,377)

Risk Factors

At least one risk factor (other than ‘unknown') was identified in 22% (172/787) of endemic cases. Of those with a reported risk factor, sexual contact and shellfish consumption were reported in 12% (21/172) and 10% (17/172) of cases, respectively. Food service was identified in 8% (14/172), and “other” risk factors were identified in 62% (106/172) of cases. For those endemic cases that reported a risk setting (404/730), 53% (215/404) identified the home as the environment where HAV was acquired. Other major risk settings included: institutions 14% (56/404), local travel 9% (37/404) and restaurant/food vendors 9% (35/404).

Although a mode of transmission was reported for 90% (709/ 787) of endemic cases, it was reported as “unknown” for the majority (65%, 467/709) of cases. Of those that reported a mode of transmission other than “unknown”, person-to-person contact (including sexual contact) was reported in 64% (154/242) of cases. Sexual contact and siblings were the two most common sources among person-to-person transmission. Those cases listing person-to-person transmission, were mostly male (62%, 96/154) and in the 20 and 49 age range (65%, 63/96). Almost 24% (15/63) of male cases in the range of 20 to 49 specified homosexual encounters. The other most commonly reported modes of transmission were food and water, accounting for 24% (58/242) and 5% (12/242) respectively.

Seventy-five percent of travel cases (443/594) specified at least one travel destination. The most commonly reported travel destination was Asia 49% (217/443). Within Asia, Pakistan and India accounted for 38% (83/217) and 28% (61/217) of cases respectively. The next most commonly reported travel destination was North America at 37% (166/443), of which, Mexico accounted for 32% (53/166) of cases and the Caribbean 20% (34/166) cases.

Discussion

The mean number of cases observed during this study period (197) was substantially lower than the mean number of cases reported previously (422) between 1992 to 2000.⁶ The total number of HAV cases dropped sharply between 1999 and 2000 mostly due to a significant decrease in the number of endemic cases. Although travel cases showed minimal fluctuation during the entire study period, the drop in the number of endemic cases created a shift in the proportion of total cases represented by travel cases. Prior to 2000, travel cases accounted for approximately 30% of all cases, in contrast to approximately 50% of cases during 2000 to 2004. In 2000, 2001 and 2003, the number of travel cases exceeded that of endemic cases.

Some possible reasons for this decrease in endemic cases include changes in immunization practices, a general decrease in food-borne illnesses and the natural HAV cycle. The observed decrease coincides with increasing availability of HAV vaccines and subsequent recommendations from the National Advisory Committee on Immunization preferring HAV vaccine over immune globulin.⁷ There is evidence that a general decrease in foodborne illnesses is occurring, most recently between 1996-1998 rates and 2005 rates in the USA.⁸ More detailed studies evaluating the influence of the vaccine are necessary to test this hypothesis. Alternatively, there is evidence of a natural 10-year cycle for HAV in the absence of any intervention⁹ suggesting that current trends seen among endemic cases in Ontario may reflect this pattern.

The number of endemic cases did not fluctuate markedly over the course of the calendar year, with the exception of a slightly lower number of reported cases in February. It is not clear what may have contributed to the low number of cases in this month. In contrast, seasonal patterns for travel cases were evident for the major travel periods during the year: the increase in April likely reflects travel during March break and the second peak in September reflects high summer travel in August. During these two periods, health units can anticipate a higher number of reported HAV cases due to travel-related reasons.

Overall, there were more male than female cases of HAV. Striking differences were found among male endemic cases in age groups 20 to 29 and 30 to 39, where age-specific rates of HAV were almost double that of females. Engaging in high-risk activities, including sexual practices, may have contributed to these high rates. Although only a modest percentage of sexual transmission was identified as being related to men having sex with men during this period, this is likely an underestimate. The reasons for under-reporting include the sensitivity of the question in a case interview and the use of free-text fields to report this risk factor in RDIS. Outbreaks in Canada have been observed among this high risk group.⁶ In addition, high susceptibility to HAV has been noted in these two age groups based on seroprevalence data. More than 90% of Canadian-born individuals aged 20 to 29 and over 80% aged 30 to 39 remain unprotected.¹⁰ The combination of susceptibility and involvement in high risk behaviours may explain the higher rates among men in these age groups.

The highest age-specific rates among travel cases were found in those aged 0 to 9 showing a decreasing rate with increasing age consistently across males and females. Males showed slightly higher rates than females. The oldest age groups had the lowest rates of HAV. This may reflect increasing herd immunity to HAV with age, or differences in travel destinations or risk behaviour, possibly due to more cautious travel among older individuals.¹¹ The death rate reported here (0.1% to 0.4%) is consistent with published death rates for HAV: average death rate ranges from 0.1% to 0.3%, although rates can increase in adults > 50 to 1.8%². Hospitalizations among HAV cases did occur, however, the majority of cases reported in this time period were not hospitalized.

The “home” was identified as the biggest risk setting for HAV among endemic cases. Person-to-person contact and food consumption, especially shellfish, were major risk factors among endemic cases. Food consumption was the most commonly cited source of infection among travel cases.

Missing, unknown or unspecified responses are a limitation when interpreting the results from this study. In addition, passive surveillance systems tend to suffer from under-reporting by the inability to detect subclinical infections among children.⁶ Children are an important source of transmission due to asymptomatic infection being common in children, poor hygiene, and the ability to shed the virus longer.^4,12 Further, mild cases are often missed in surveillance systems since they may not seek medical attention. Thus, the true incidence and burden of illness is not fully captured through passive surveillance systems. Despite these limitations, the results from this study offer important information on the epidemiology of endemic and travel HAV cases in Ontario.

Conclusion

There has been a substantial decrease in the number of endemic cases of HAV in Ontario, contributing an overall decrease in total reported cases. Since seasonal trends were mostly observed among travel cases, health units may observe an increase in HAV during the months of April and September.

Acknowledgements

The authors thank the following for their assistance: Dr. D. Middleton, Ontario Ministry of Health and Long-Term Care, Toronto, Ontario, S. Johnson, Ontario Ministry of Health and Long-Term Care, Toronto, Ontario, private laboratories, Public Health Laboratories, and the Ontario Public Health Units.

References

1. Cuthbert J. Hepatitis A: Old and new. Clin Microbiol Rev 2001;14:38-58.

2. Heymann DL. (Ed.) Control of Communicable Disease Manual. 18th ed. American Public Health Association: Washington DC. 2004.

3. Leach C. Hepatitis A in the United States. Pediatr Infect Dis J 2004;23:551-2.

4. Edgar B, Buxton JA. A review of provincial/territorial strategies for hepatitis A pre- and post- exposure prophylaxis. CCDR. 2005;31:197-205.

5. Government of Ontario. Health Protection and Promotion Act. Revised Statutes of Ontario, 1990. Section 1(1). Sept 19, 2003. Queen's Printer for Ontario.

6. Wilson S, Middleton D. Epidemiology of hepatitis A in Ontario, 1992-2000. PHERO. 2002;13:41-6.

7. Health Canada. Supplementary statement on hepatitis A vaccine. CCDR. 2000;26(ACS-4):12-8.

8. Centers for Disease Control and Prevention. Preliminary FoodNet Data on the Incidence of Infection with Pathogens Transmitted Commonly Through Food - 10 States, United States, 2005. MMWR 2006;55:392-5.

9. Centers for Disease Control and Prevention. Prevention of hepatitis A through active or passive immunization: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 2006;55:1-23.

10. Pham B, Duval B, De Serres G et al. Seroprevalence of hepatitis A infection in a low endemicity country: A systematic review. BMC Infect Dis 2005;5:55-66.

11. De Serres G, Duval B, Shadmani RL et al. Ineffectiveness of the current strategy to prevent hepatitis A in travelers. J Travel Med 2002;9:10-6.

12. Armstrong G, Bell B. Hepatitis A virus infections in the United States: Model-based estimates and implications for childhood immunization. Pediatrics. 2002;109:839-45.

[Table of Contents] [Next]