During the study (November 1, 1996, to January 31, 1999), the Communicable Disease Control Section of BSPHU served a population of approximately 1.1 million persons in several local government areas, south Brisbane (part of the Brisbane City Council Area), Logan, Redlands, Beaudesert, and Gold Coast (12). All persons who reported a potential ABL exposure (bat bite, scratch, percutaneous, or permucosal exposure to bat saliva or neural tissue) were asked to complete a standard questionnaire, which sought demographic information (including occupation, history of professional or volunteer bat handling, history of rabies vaccination, potential rabies exposure [bite, scratch, provoked, unprovoked], circumstances that led to the exposure, treatment received, and any laboratory investigation of the bat).

A separate questionnaire was completed for each occasion a person contacted BSPHU to report potential ABL exposure. Potential exposures were reported retrospectively, and the dates of notification and potential exposure for each case were included. All information was recorded and analyzed by using an Epi-Info 6.04b database (13). Age and gender-specific notification rates were calculated by using estimated resident population data for 1997 (12).

During the same period, healthy bats, sick and injured bats, and bats involved in a potential human exposure to ABL were tested for infection with a fluorescein-labeled antirabies monoclonal globulin (CENTOCOR) in a direct fluorescent antibody test (DFAT) on fresh brain impression smears at the Queensland Department of Primary Industries Animal Research Institute or at the CSIRO Australian Animal Health Laboratories. Material from most bats that tested positive for ABL infection and from bats associated with a potential human exposure to ABL were sent to either the Australian Animal Health Laboratory or Queensland Health Scientific Services for confirmation by DFAT, virus isolation, and polymerase chain reaction.

Figure 1

Figure 1. Age and gender-specific average annual notification rates of potential human exposure to Australian bat lyssavirus (n = 204) South Brisbane and South Coast, Queensland, 1996-1999.

Figure 2

Figure 2. Dates of potential Australian bat lyssavirus exposures and notifications to the Brisbane Southside Public Health Unit, south Brisbane and South Coast, Queensland, 1996-1999.

A total of 205 notifications to BSPHU met the criteria for potential ABL exposure during the study period, an average annual notification rate of 8.1/100,000. Complete information was obtained from 202 persons. Total notifications included 86 males and 119 females (M:F ratio of 1:1.38). The age- and gender-specific average annual notification rates are presented in Figure 1. Most reported potential exposures (116 of 204) were among persons 19 to 49 years of age. The months of potential ABL exposure and notification are presented in Figure 2. Most notifications (131 of 205) were made within 2 months of each of the two fatal human cases. Nine (11%) of 80 notifications made in the 2 months following the first reported case were related to exposures that occurred >2 months before the first human case was publicized. The median interval between exposure and notification of these 80 potential exposures was 17 days (0 to 1,080 days). In the 2 months following the second case, 22 (43%) of 51 notifications were related to potential exposures that had occurred before the reporting of the first human case. The median interval between exposure and notification of the 51 potential exposures was 728 days (0 to 2,907 days). A further 14 (27%) of the 51 notifications were related to potential exposures that had occurred since the first human case but had not been reported to BSPHU at the time of exposure.

This is the first description of PEP provided to an Australian community after the recognition of human risk for ABL infection. The first human case triggered a large national public health campaign and considerable public awareness about the risks from bats, particularly in communities such as south Brisbane and the South Coast of Queensland, where large colonies of bats live close to human urban populations and bat/human interaction is not uncommon. Increased concern was demonstrated by the large number of notifications of potential exposure that followed reports of the two human cases (Figure 2). Most potential human exposures were among adults (ages 25 to 49). The increased proportion of women reflects the high proportion of female volunteer bat handlers in the study population.

The first 2 months of notifications represents a catch-up period in which PEP was provided to persons with exposures dating back several years. Relatively few notifications occurred after the first 2 months of the study, and it was only after the second human case, which had an assumed incubation period of approximately 2 years, that another cluster of notifications occurred (4). The median interval between potential exposure and notification increased from 17 days for those notified in the 2 months after the first human ABL case to 728 days for those notified in the 2 months after the second case. The potential exposures reported in the 2 months after the second case included 22 persons who were potentially exposed before the first case and 14 with >1 month between potential exposure and notification. The second human case with its prolonged incubation period reinforced the public perception of the severity of this disease and prompted more notifications.

Potential exposures occurred most commonly in spring and summer, coinciding with the birthing season (October to December) of the black and grey-headed flying foxes in southeastern Queensland (15). During each birthing season in southeastern Queensland, 100 to 300 neonatal and juvenile black or grey-headed flying foxes are reared by volunteer bat handlers (H. Luckhoff, pers. comm.). These orphans are commonly assumed to have been abandoned or separated from their dams. Frequently, orphans are found still clinging to the body of their dam. Further research is required to identify any association between orphaned bats and the ABL status of the dam. A case of clinical disease in an in-care juvenile black flying fox and the associated exposure of eight humans has been described (6).

Most potential exposures (107 [52%] of 205) were reported from groups who handled bats. These groups were the target of initial public health information campaigns to raise awareness of the risks for ABL infection. PEP was provided to members of these groups after the first human case, and a recommendation was issued that all workers in these fields be vaccinated with HDCV and that unvaccinated persons, including family members of volunteer bat handlers, not handle bats. Seventy-two (35%) of 205 potential exposures occurred among members of the community. Most of these (63 [88%] of 72) had rescued a trapped or fallen bat. The test results from bats indicate that sick, injured, or orphaned bats have a significantly higher crude prevalence of ABL infection (p <0.001) than healthy wild-caught or captive bats. Consequently, the risk for ABL exposure among volunteer and professional bat handlers and persons who rescue bats may be relatively increased because these groups primarily handle sick, injured, or orphaned bats.

Reporting of potential exposures among groups at risk changed with time during the study. One important factor in the management of PEP was the requirement (introduced in 1997) that all bats involved in a potential human exposure be surrendered for postmortem examination and laboratory testing for ABL. Those who care for bats are often reluctant to surrender them for ABL testing. Notifications from volunteer bat handlers declined during the study period. While this may reflect a decline either in the number of bat handlers or in potential exposures among volunteer bat handlers, underreporting may be occurring in this group. Anecdotal evidence suggests that this reduction in notifications may reflect handlers' concern for the bats. Such underreporting could be associated with future human cases. Most potential exposures resulted from intentional handling of bats. The few potential exposures from unprovoked encounters suggest that bats rarely initiate contact with humans.

The recognition of ABL infection has resulted in a large public health program to provide education, counseling, and prophylaxis to volunteer and professional bat handlers and members of the community who may be exposed to ABL. The focus of the program has been to encourage preexposure vaccination of bat handlers, prevention of potential exposures by avoidance of bat handling by nonvaccinated persons, and prompt medical care when potential exposures occur. The cost of PEP for all those potentially exposed to ABL in south Brisbane and the South Coast of Queensland during the study was considerable. Future public health interventions should continue to emphasize the risks associated with interaction with bats to reduce the requirement for PEP and the likelihood of human cases of ABL infection.