Mass Treatment of Humans Exposed to Rabies -- New Hampshire, 1994

On October 22, 1994, the laboratory of the New Hampshire Division of Public Health Services (NHDPHS) diagnosed rabies in a kitten that had been purchased from a pet store in Concord, New Hampshire. On October 19, the animal had developed seizures, then died of unknown causes during the night of October 20-21. Approximately 665 persons received rabies postexposure prophylaxis because of exposure to this kitten and other cats from the same pet store. This report summarizes the epidemiologic investigation of the source of the infection and follow-up care of humans and animals potentially exposed to rabies.

Because the pet store did not keep records for kittens acquired for sale, the kitten's origin and date of arrival were unknown. However, on September 26, a group of kittens reported to have included the rabid kitten was examined by a veterinarian and given health certificates, in accordance with state law, before being offered for sale by the pet store. The kitten was sold on October 5 and kept by its owners until its death. On October 22, rabies was diagnosed in the kitten by fluorescent antibody testing at the NHDPHS laboratory. At CDC, genetic typing of the rabies virus isolated from the kitten indicated that it was a variant associated with raccoons. The investigation could not determine whether the kitten was infected with rabies before, during, or after its stay in the pet store; two other kittens sold by the pet store during the same period as the infected kitten died of unknown causes at their new homes but were unavailable for testing for rabies.

On October 12, a raccoon captured in Henniker (a suburb of Concord), where the kitten was suspected to have originated, tested positive for rabies. Subsequent investigation indicated that the raccoon may have had direct contact with three feral kittens acquired by the pet store on September 20. All three feral kittens developed signs of respiratory illness and died during approximately October 4-October 6 -- a period overlapping that during which the rabid kitten was in the store. None of these three kittens were available for testing for rabies and all were younger than the minimum age (3 months) recommended for rabies vaccination.

From September 19 through October 23 (the last date any potentially exposed kittens were in the pet store), a minimum of 34 kittens had been offered for sale by the store. In addition to the infected kitten, 33 other kittens were included in the investigation: 27 were located and tested negative for rabies, and five died of unknown causes but were unavailable for testing (including the three feral kittens); one kitten was quarantined at the owner's request, and its status is unknown.

Because of limitations in the store's records regarding the origins and sale destinations of the kittens, local news media assisted in alerting community residents about the potential exposures to rabies at the store. The kittens had been allowed to roam freely throughout the store, which was frequented by children from child-care centers and a nearby school. As a result, NHDPHS and two major health-care facilities screened approximately 1000 persons who responded to media alerts and referred to private sector health-care providers for definitive evaluation of those persons who might need rabies postexposure treatment. NHDPHS gave medical providers an algorithm to determine the necessity for recommending rabies postexposure treatment. Rabies postexposure treatment, consisting of one dose of rabies immune globulin and five doses of rabies vaccine, was initiated for approximately 665 persons (1). Reported by: M Klauber, Dartmouth-Hitchcock Medical Center, Concord; C McGinnis, DVM, New Hampshire Dept of Agriculture; RT DiPentima, MPH, AE Burns, MS, VC Malmberg, MS, JS Finnigan, MJ Walsh, JE Whitcomb, CE Danielson, MD, MG Smith, MD, State Epidemiologist, Div of Public Health Svcs, New Hampshire Dept of Health and Human Svcs. Viral and Rickettsial Zoonoses Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: This incident of rabies associated with a pet store resulted in the largest number of persons ever reported to have received rabies postexposure treatment as a result of potential contact with a point source in the United States. * At least three factors accounted for the large number of persons requiring treatment. First, the absence of pet store records regarding the source and destination of animals precluded an accurate estimation of the exposure period. Second, the store's popularity and its practice of allowing kittens to roam freely throughout the establishment increased contacts between humans and kittens. Finally, because many children were potentially exposed, accurate exposure histories could not be elicited; as a consequence, many rabies postexposure treatments were administered on the basis of incomplete information or unknown likelihood of exposure.

The costs associated with the public health response to exposures to the rabid kitten in New Hampshire are unprecedented in the United States. The overall estimated cost was $1.5 million, including expenditures for rabies immune globulin and vaccine ($1.1 million), laboratory testing of animals ($4200), and investigation by NHDPHS and CDC personnel ($15,000). This cost is nearly 15-fold higher than that ($105,790) associated with rabies postexposure treatment of 70 persons after a single case of rabies occurred in a domestic dog in California in 1981 (2).

CDC recommends implementation of four measures to minimize the number of exposed persons and the costs associated with exposures to persons. First, to facilitate efforts to investigate such exposures, pet stores should keep adequate records (e.g., health certificates, animal source identification, and complete sales receipts). Second, to prevent the exposure to, or the transmission of, rabies and other zoonotic diseases -- as well as injuries such as bites and scratches -- animals should be kept and displayed separate from customers or at least confined to a discrete area within the store. Third, because feral animals are less likely to have been vaccinated and more likely to have been in contact with wildlife disease reservoirs, acquisition and sale of these animals should be monitored closely. Finally, prompt and standardized assessment of exposure by public health officials should help minimize the number of persons who unnecessarily receive rabies postexposure treatment. The rabies virus is transmitted only when introduced into open wounds or mucous membranes through a bite or direct saliva contact. Other forms of contact (e.g., petting a rabid animal or contact with blood, urine, or feces of a rabid animal) do not constitute an exposure and are not indications for prophylaxis (1). Skillful interviewing is essential to assess individual exposures, especially when the potential exposure occurred some time ago or in another family member (e.g., a young child).

The rabid kitten involved in this incident had been infected with a rabies virus variant usually associated with raccoons. Since 1977, a raccoon rabies epizootic has spread from a focus in West Virginia to involve all eastern region states (3). During 1993, nearly 6000 raccoons were confirmed with rabies in this region. Although no human rabies cases have been associated with this epizootic, the economic burden related to postexposure prophylaxis has been high. This epizootic and case described in this report underscore the need for intensification of rabies-control measures, including vaccination of all household pets.

References

1. ACIP. Rabies prevention -- United States, 1991: recommendations of the Immunization Practices Advisory Committee (ACIP). MMWR 1991;40(no. RR-3).

2. CDC. The cost of one rabid dog -- California. MMWR 1981;30:527.

3. Krebs JW, Strine TW, Smith JS, Rupprecht CE, Childs JE. Rabies surveillance in the United States during 1993. J Am Vet Med Assoc 1994;205:1695-1709.

• On June 22, a second episode of rabies in a kitten associated with a pet store was reported by the Delaware Department of Health and Social Services. Through June 30, approximately 18 persons had received postexposure prophylaxis for potential rabies exposure. An investigation of this incident is ongoing.

  
  

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