Rabies exposure incidence calculation

The annual incidence of suspected animal bites can be calculated from the community level animal bite incidence and the observed proportion of suspected bites in the health centres during the observation period. The incidence of suspected animal bites can be related to the recorded number of rabid animals in the same study area during the same period.

By maximising communication between the public health providers and animal health authorities, the number of suspected dogs can be related as closely as possible to the number of aetiologically confirmed rabid animals. In this way, the level of underreporting and the true incidence can be assessed. For every rabid animal, the number of exposed humans can be established and followed up to also identify further exposures along a snowball principle.

In the table below, a simplified fully calculated example for an urban and a rural zone shows how three study types a) household, b) health centre and c) animal diagnostic laboratory are inextricably linked in order to estimate ascertained rabid bites with lower confidence limits. Using a backward extrapolation to the population level incidence of ascertained rabid animal bites, the total number of rabies exposures and clinical cases and the unmet demand for post-exposure prophylaxis (PEP) is demonstrated with the respective sources of information, assumptions and calculations.

^{Rabies incidence calculated example for an urban and rural zone
© Jakob Zinsstag}

This example shows that the estimation of human rabies incidence estimation requires a close cooperation between the public and animal health sector. An integrated One Health assessment allows the estimation of the true incidence of exposure.

References

Cleaveland, S. et al. (2002). Estimating Human Rabies Mortality in the United Republic of Tanzania from Dog Bite Injuries, in: Bulletin of the World Health Organization 80(4), 304-310.

Frey, J. et al. (2013). Survey of Animal Bite Injuries and their Management for an Estimate of Human Rabies Deaths in N’Djamena, Chad, in: Tropical Medicine & International Health 18(12), 1555-62.

Kayali, U. et al. (2003). Incidence of Canine Rabies in N’Djamena, Chad, in: Preventive veterinary medicine 61(3), 227-233.