Animal-based national surveillance for zoonotic disease: quality, limitations, and implications of a model system for monitoring rabies.

Surveillance for zoonotic diseases among wildlife is a research and public health challenge. The inherent limitations posed by the requisite human-animal interactions are often undefined and underappreciated. The national surveillance system for animal rabies in the United States was examined as a model system; reporting of animal rabies is legally mandated, each case of rabies is laboratory confirmed, and data have been consistently collected for more than 50 years. Factors influencing the monthly counts of animal rabies tests reported during 1992-2001 were assessed by univariate and multivariable regression methods. The suitability of passively collected surveillance data for determining the presence or absence of the raccoon-associated variant of rabies within states and within individual counties was assessed by determining critical threshold values from the regression analyses. The size of the human population and total expenditures within a county accounted for 72% and 67%, respectively, of the variance in testing. The annual median number of rabies tests performed was seven for counties without rabies, 22 for counties with non-raccoon rabies, and 34 for counties with raccoon rabies. Active surveillance may be required in locales with sparse human populations when a high degree of confidence in the status of rabies is required.

Human monocytic ehrlichiosis and human granulocytic anaplasmosis in the United States, 2001-2002.

The epidemiologic features are described of cases of human monocytic ehrlichiosis and human granulocytic anaplasmosis in the United States.

Persistence of elevated rabies prevention costs following post-epizootic declines in rates of rabies among raccoons (Procyon lotor).

Determining the benefits to cost relationships among different approaches to rabies control and prevention has been hindered by the inherent temporal variability in the dynamics of disease among wildlife reservoir hosts and a tangible and objective measure of the cost of rabies prevention. A major and unavoidable component of rabies prevention programs involves diagnostic testing of animals and the subsequent initiation of appropriate public health responses. The unit cost per negative and positive diagnostic test outcome can be reasonably estimated. This metric when linked to methodologies subdividing the epizootic process into distinct temporal stages provided the requisite detail to estimate benefits derived from rabies control strategies. Oral rabies vaccine (ORV), for prevention of the raccoon-associated variant of rabies, has been distributed in Ohio and adjoining states in an effort to develop an immune barrier to the westward spread of epizootic raccoon rabies. The costs of ORV delivery have been quantified. Herein, the cost structures required to assess the benefits accrued by prevention were developed. A regression model was developed effectively predicting (r2=0.70) the total number of rabies diagnostic tests performed by 53 counties in five northeastern (NE) states from 1992 to 2001. Five temporal stages sufficed to capture the range of variability in the raccoon rabies epizootic process. Unit costs, dollars per diagnostic test outcome, were calculated for negative and positive results from published reports. Ohio counties were matched to NE counties based on similar socioeconomic characters. A "pseudo-epizootic" of raccoon rabies was introduced into Ohio and the costs savings from ORV were derived as the excess costs imposed by epizootic spread throughout the state. At 46 km/year (range modeled, 30-60 km/year), the pseudo epizootic spread, and reached the enzootic stage, in all Ohio counties by year 13 (range modeled, 11-17 years). Cumulative excess costs for Ohio ranged between $11 and $21 million; counties of low socioeconomic status experienced the greatest relative excess costs. The costs for rabies prevention activities reached apices during the epizootic stage of raccoon rabies (2.7-10.8 times baseline) an unforeseen finding indicated elevated costs persisted (1.7-7.2 times baseline) into the enzootic stage.

Temporal dynamics of rabies in a wildlife host and the risk of cross-species transmission.

An epidemiological model was developed for rabies, linking the risk of disease in a secondary species (cats) to the temporal dynamics of disease in a wildlife reservoir (raccoons). Data were obtained from cats, raccoons, and skunks tested for rabies in the northeastern United States during 1992-2000. An epizootic algorithm defined a time-series of successive intervals of epizootic and inter-epizootic raccoon rabies. The odds of diagnosing a rabid cat during the first epizootic of raccoon rabies was 12 times greater than for the period prior to epizootic emergence. After the first raccoon epizootic, the risk for cat rabies remained elevated at levels six- to seven-fold above baseline. Increased monthly counts of rabid raccoons and skunks and decreasing human population density increased the probability of cat rabies in most models. Forecasting of the public health and veterinary burden of rabies and assessing the economics of control programmes, requires linking outcomes to dynamic, but predictable, changes in the temporal evolution of rabies epizootics.

Analysis of risk factors for fatal Rocky Mountain Spotted Fever: evidence for superiority of tetracyclines for therapy.

Epidemiologic and clinical characteristics of fatal and nonfatal cases of Rocky Mountain spotted fever (RMSF) were compared to identify risk factors for death caused by this disease. Confirmed and probable RMSF cases reported through US national surveillance for 1981-1998 were analyzed. Among 6388 RMSF patients, 213 died (annual case-fatality rate, 3.3%; range, 4.9% in 1982 to 1.1% in 1996). Use of tetracycline-class antibiotics for treatment of RMSF increased significantly in the 1990s, compared with use in the 1980s. Older patients, patients treated with chloramphenicol only, patients for whom tetracycline antibiotics were not the primary therapy, and patients for whom treatment was delayed > or =5 days after the onset of symptoms were at higher risk for death. Although the case-fatality rate was lower in the 1990s than in the 1980s, risk factors for fatal RMSF were similar. Despite the availability of effective antibiotics, RMSF-related deaths continue to occur because of delayed diagnosis and failure to use appropriate therapy.

Rabies epizootics among raccoons vary along a North-South gradient in the Eastern United States.

The characteristics of rabies epizootics among raccoons were investigated in 11 eastern states along a North-South gradient from New York to North Carolina. Epizootics were defined as discrete intervals of time of at least 5 months in duration, when reported cases of raccoon rabies from an individual county exceeded the median value of raccoon rabies cases reported by that county over the entire period rabies was present among raccoons in the county. Over the approximately 20-year study period, 35,000 cases of raccoon rabies were reported, and epizootics were detected from 251 (64.4%) of 390 counties. The median annual incidence was 0.14 epizootics per year. During the first defined epizootic in a county, the median total number of raccoons reported rabid was 47, with a median monthly incidence of rabies in raccoons of 3.1. The median lag time from the first report of a rabid raccoon in a county to the beginning of the first epizootic was 4 months. Significant differences in the annual incidence of epizootics and monthly incidence of rabid raccoons during epizootics were observed among different states. Although human population density and per capita health spending within counties were positively associated with increasing magnitude of epizootics, a significant difference in the characteristics of rabies epizootics in northern and southern states was apparent. We hypothesize that environmental conditions and perhaps human influence resulted in rabies epizootics in southern states that were smaller, less-frequent, and lacking in well-defined temporal structure compared with those in northern states.

Rabies surveillance in the United States during 2000.

During 2000, 49 states, the District of Columbia, and Puerto Rico reported 7,364 cases of rabies in nonhuman animals and 5 cases in human beings to the Centers for Disease Control and Prevention, an increase of 4.3% from 7,067 cases in nonhuman animals reported in 1999. Ninety-three percent (6,855 cases) were in wild animals, whereas 6.9% (509 cases) were in domestic species (compared wth 91.5% in wild animals and 8.5% in domestic species in 1999). Compared with cases reported in 1999, the number of cases reported in 2000 increased among bats, dogs, foxes, skunks, and sheep/goats and decreased among cats, cattle, horses/mules, raccoons, and swine. The relative contributions of the major groups of animals were as follows: raccoons (37.7%; 2,778 cases), skunks (30.2%; 2,223), bats (16.8%; 1,240), foxes (6.2%; 453), cats (3.4%; 249), dogs (1.6%; 114), and cattle (1.1%; 83). Ten of the 19 states where the raccoon-associated variant of the rabies virus has been enzootic reported increases in the numbers of cases of rabies during 2000. Among those states that have engaged in extensive wildlife rabies control programs, no cases of rabies associated with the epizootic of rabies in raccoons (or in any other terrestrial species) were reported in Ohio, compared with 6 cases reported in 1999. No rabies cases associated with the dog/coyote variant (compared with 10 cases in 1999, including 5 in dogs) were reported in Texas, and cases associated with the gray fox variant of the virus decreased (58 cases in 2000, including 38 among foxes). Reports of rabid skunks exceeded those of rabid raccoons in Massachusetts and Rhode Island, states with enzootic raccoon rabies, for the fourth consecutive year. Nationally, the number of rabies cases in skunks increased by 7.1% from that reported in 1999. The greatest numerical increase in rabid skunks (550 cases in 2000, compared with 192 in 1999) was reported in Texas. The number of cases of rabies reported in bats (1,240) during 2000 increased 25.4% over the number reported during 1999 (989) and represented the greatest contribution (16.8% of the total number of rabid animals) ever recorded for this group of mammals. Cases of rabies reported in cattle (83) and cats (249) decreased by 38.5% and 10.4%, respectively, whereas cases in dogs (114) increased by 2.7% over those reported in 1999. Reported cases of rabies among horses and mules declined 20% from 65 cases in 1999 to 52 cases in 2000. Four indigenously acquired cases of rabies reported in human beings were caused by variants of the rabies virus associated with bats. One case of human rabies acquired outside the United States that resulted from a dog bite was caused by the canine variant of the rabies virus.

Predicting the local dynamics of epizootic rabies among raccoons in the United States.

Mathematical models have been developed to explore the population dynamics of viral diseases among wildlife. However, assessing the predictions stemming from these models with wildlife databases adequate in size and temporal duration is uncommon. An epizootic of raccoon rabies that began in the mid-Atlantic region of the United States in the late 1970s has developed into one of the largest and most extensive in the history of wildlife rabies. We analyzed the dynamics of local epizootics at the county level by examining a database spanning more than 20 years and including 35,387 rabid raccoons. The size, number, and periodicity of rabies epizootics among raccoons were compared with predictions derived from a susceptible, exposed, infectious, and recovered model of raccoon rabies [Coyne, J., Smith, G. & McAllister, F. E. (1989) Am. J. Vet. Res. 50, 2148-2154]. After our methods for defining epizootics were applied to solutions of the model, the time series revealed recurrent epizootics in some counties, with a median first epizootic period of 48 months. Successive epizootics declined in size and the epizootic period progressively decreased. Our reanalysis of the model predicted the initial-epizootic period of 4-5 years, with a progressive dampening of epizootic size and progressive decrease in epizootic period. The best quantitative agreement between data and model assumed low levels of immunity (1-5%) within raccoon populations, suggesting that raccoons develop little or no rabies immune class. These results encourage the use of data obtained through wildlife surveillance in assessing and refining epidemic models for wildlife diseases.

Survey of rabies preexposure and postexposure prophylaxis among missionary personnel stationed outside the United States.

BACKGROUND: Of the 36 cases of human rabies that have occurred in the United States since 1980, 12 (33%) were presumed to have been acquired abroad. In the United States, it is recommended that international travelers likely to come in contact with animals in canine rabies-enzootic areas that lack immediate access to appropriate medical care, including vaccine and rabies immune globulin, should be considered for preexposure prophylaxis. In 1992, the death of an American missionary who had contracted rabies while stationed in Bangladesh highlighted this high-risk group. METHODS: To assess their knowledge of rabies risk, rabies exposures, and compliance with preventive recommendations, we asked 695 missionaries and their family members to complete questionnaires about their time stationed abroad. RESULTS: Of the 293 respondents stationed in countries where rabies is endemic, 37% reported prior knowledge of the presence of rabies in their country of service. Only 28% of the personnel stationed in rabies-endemic countries received preexposure prophylaxis. Having preexposure prophylaxis specifically recommended increased the likelihood of actually receiving it (O.R. 15.6, 95%CI 7.4 - 34.9). There were 38 reported exposures (dogs = 66%, another human = 20%), proven or presumed to be rabid. Three of the people exposed received rabies immune globulin and vaccine; 11 received vaccine alone; 8 received only basic first aid, and 16 received no treatment. CONCLUSIONS: Although American missionaries stationed abroad are at an increased risk for exposure to rabies, compliance with established preventive measures was low. Prior to being stationed abroad, an educational rabies-prevention briefing, including encouragement to receive preexposure prophylaxis, could be an effective intervention for missionaries to decrease their risk of rabies.

Mammalian reservoirs and epidemiology of rabies diagnosed in human beings in the United States, 1981-1998.

Between 1981 and 1998, 37 cases of rabies were diagnosed in human beings in the United States. Information directly linking the cause of infection to animal bite was available for only eight of these cases. Indirect incrimination of the vector by analysis of cDNA sequences obtained by reverse transcriptase polymerase chain reaction of samples indicated that for all cases (12/12) believed to have been acquired in foreign countries, variants of the rabies virus (VRVs) associated with dogs (7/12 involved known bite histories) were the cause of the rabies infections. In contrast, VRVs associated with bats (bat-associated VRVs or BAVs) were implicated as the cause of 88% (22/25) of infections believed to have been acquired within the United States (1/22 involved known bite histories). Sequence analyses revealed that a single BAV (Ln/Ps), associated with rabid silver-haired (Lasionycteris noctivagans) and Eastern pipistrelle (Pipistrellus subflavus) bats, was implicated in 73% (16/22) of bat-associated infections. Silver-haired bats are predominantly solitary and migratory. Eastern pipistrelle bats may occur individually or in small clusters. Both species are only infrequently submitted for rabies testing. Unrecognized bites and unique properties of the Ln/Ps BAV may explain its association with the majority of rabies infections in human beings in the United States.

Rabies surveillance in the United States during 1999.

During 1999, 49 states, the District of Columbia, and Puerto Rico reported 7,067 cases of rabies in nonhuman animals to the Centers for Disease Control and Prevention, a decrease of 11.2% from 7,961 cases in nonhuman animals and 1 case in a human being reported in 1998. More than 91% (6,466 cases) were in wild animals, whereas 8.5% (601 cases) were in domestic species (compared with 92.4% in wild animals and 7.6% in domestic species in 1998). No cases of rabies were reported in human beings in 1999. Decreases were evident in all major species groups, with the exception of cattle, sheep/goats, and swine. The relative contributions of the major groups to the total reported were as follows: raccoons (41.0%; 2,872 cases), skunks (29.4%; 2,076), bats (14.0%; 989), foxes (5.4%; 384), cats (3.9%; 278), cattle (1.9%; 135), and dogs (1.6%; 111). Reported cases (6) associated with the epizootic of rabies in raccoons in Ohio declined from the 26 cases reported in 1998. Fifteen of the 19 states where the raccoon variant of the rabies virus is enzootic reported fewer cases of rabies during 1999. Massachusetts and Rhode Island, states with enzootic rabies in raccoons, each reported more rabid skunks than rabid raccoons for the third consecutive year. In Texas, cases associated with the enzootic canine variants of the rabies virus remained low (10 cases), whereas cases associated with the gray fox variant of the virus increased (66). Cases of rabies in skunks decreased by 8.6%, compared with those reported in 1998. Michigan reported the largest percentage increase in rabid skunks (950.0%; 2 cases in 1998 to 21 in 1999). Cases of rabies in horses and mules declined 21%, from 82 cases in 1998 to 65 in 1999. Cases of rabies reported in bats (989) were similar in number to those reported in 1998 (992) and represented almost 14.0% of the total number of rabid animals reported during 1999. Reported cases of rabies in cats (278) and dogs (111) decreased by 1.4% and 1.8%, respectively, whereas cases in cattle (135) increased by 16.4%, compared with those reported in 1998.

Rocky Mountain spotted fever in the United States, 1993-1996.

During 1993 through 1996, 2,313 cases of Rocky Mountain spotted fever (RMSF) were reported to the Centers for Disease Control and Prevention (CDC) by 42 states and the District of Columbia through the National Electronic Telecommunications System for Surveillance (NETSS). During this same interval, 1,752 case report forms (CRFs) were submitted to CDC and 1,253 (70%) of the cases were categorized as confirmed RMSF by laboratory testing. On the basis of analyses performed with NETSS data, the average annual RMSF incidence during 1993-1996 was 2.2 cases per million persons; the incidence rose from 1.8 in 1993 to 3.3 per million persons in 1996. Incidence for confirmed cases was highest among children 5-9 years of age (3.7 per million) and lowest among individuals older than 70 years of age (1.4 per million). The south Atlantic region accounted for the largest proportion of confirmed cases (52%). The case-fatality rate was highest among persons 70 years of age and older (9.0%) and lowest among adults 40-49 years of age (0.6%).

Rabies surveillance in the United States during 1998.

During 1998, 49 states, the District of Columbia, and Puerto Rico reported 7,961 cases of rabies in nonhuman animals and 1 case in a human being to the Centers for Disease Control and Prevention, a decrease of 6.5% from 8,509 cases in nonhuman animals and 4 cases in human beings reported in 1997. More than 92% (7,358 cases) were in wild animals, whereas > 7.5% (603 cases) were in domestic species (compared with 93% in wild animals and 7% in domestic species in 1997). Decreases were evident in all of the major contributing species groups, with the exception of skunks and bats. The relative contributions of the major groups to the total reported for 1998 were reccoons (44.0%; 3,502 cases), skunks (28.5%; 2,272), bats (12.5%; 992), foxes (5.5%; 435), cats (3.5%; 282), cattle (1.5%; 116), and dogs (11.5%; 113). No further discernable westward extension of the epizootic of rabies in raccoons in Ohio was reported. Twelve of the 19 states enzootic for the raccoon variant of the rabies virus and the District of Columbia reported decreased numbers of cases of rabies during 1998, compared with 13 states and the District of Columbia that reported increases during 1997. Three states, Rhode Island (143.2%), Massachusetts (77.2%), and New Hampshire (69.4%), reported increases of > 50% during 1998, compared with totals reported for 1997. In Texas, the number of cases of rabies associated with enzootic canine variants of the rabies virus remained greatly diminished; however, overall totals of reported cases of rabies increased in Texas and 12 other states where skunks are the major terrestrial reservoir of rabies. At the national level, the total of 82 reported cases of rabies among horses and mules was greater than that reported for any year since 1981 (88 cases) and represented a 74.5% increase, compared with the total for 1997. The 992 cases of rabies reported in bats during 1998 were the greatest proportionate contribution by bats since 1990. Reported cases of rabies in cats (282), dogs (113), and cattle (116) decreased 6.0%, 10.3%, and 4.9%, respectively. One indigenously acquired case of rabies reported in a human being during 1998 was the result of infection with a rabies virus variant associated with silver-haired and eastern pipistrelle bats.

Hidden mortality attributable to Rocky Mountain spotted fever: immunohistochemical detection of fatal, serologically unconfirmed disease.

Rocky Mountain spotted fever (RMSF) is the most severe tickborne infection in the United States and is a nationally notifiable disease. Since 1981, the annual case-fatality ratio for RMSF has been determined from laboratory-confirmed cases reported to the Centers for Disease Control and Prevention (CDC). Herein, a description is given of patients with fatal, serologically unconfirmed RMSF for whom a diagnosis of RMSF was established by immunohistochemical (IHC) staining of tissues obtained at autopsy. During 1996-1997, acute-phase serum and tissue samples from patients with fatal disease compatible with RMSF were tested at the CDC. As determined by indirect immunofluorescence assay, no patient serum demonstrated IgG or IgM antibodies reactive with Rickettsia rickettsii at a diagnostic titer (i.e., >/=64); however, IHC staining confirmed diagnosis of RMSF in all patients. Polymerase chain reaction validated the IHC findings for 2 patients for whom appropriate samples were available for testing. These findings suggest that dependence on serologic assays and limited use of IHC staining for confirmation of fatal RMSF results in underestimates of mortality and of case-fatality ratios for this disease.

Search for the Ebola virus reservoir in Kikwit, Democratic Republic of the Congo: reflections on a vertebrate collection.

A 3-month ecologic investigation was done to identify the reservoir of Ebola virus following the 1995 outbreak in Kikwit, Democratic Republic of the Congo. Efforts focused on the fields where the putative primary case had worked but included other habitats near Kikwit. Samples were collected from 3066 vertebrates and tested for the presence of antibodies to Ebola (subtype Zaire) virus: All tests were negative, and attempts to isolate Ebola virus were unsuccessful. The investigation was hampered by a lack of information beyond the daily activities of the primary case, a lack of information on Ebola virus ecology, which precluded the detailed study of select groups of animals, and sample-size limitations for rare species. The epidemiology of Ebola hemorrhagic fever suggests that humans have only intermittent contact with the virus, which complicates selection of target species. Further study of the epidemiology of human outbreaks to further define the environmental contact of primary cases would be of great value.

Rabies surveillance in the United States during 1997.

In 1997, 49 states, the District of Columbia, and Puerto Rico reported 8,509 cases of rabies in nonhuman animals and 4 cases in human beings to the Centers for Disease Control and Prevention. Nearly 93% (7,899) were wild animals, whereas 7% (610) were domestic species. The total number of reported cases increased 19.4% from that of 1996 (7,128 cases). Increases were apparent in each of the major species groups, with the exception of cattle. The relative contributions of these groups to the total reported for 1997 were as follows: raccoons (50.5%; 4,300 cases), skunks (24.0%; 2,040), bats (11.3%; 958), foxes (5.3%; 448), cats (3.5%; 300), dogs (1.5%; 126), and cattle (1.4%; 122). The 958 cases of rabies reported in bats represented a 29.3% increase over the total reported for 1996 and the greatest number reported since 1984, with cases reported by 46 of the 48 contiguous states. The epizootic of rabies in raccoons expanded into Ohio in 1997 and now includes 19 states and the District of Columbia. Thirteen states, where rabies in raccoons is enzootic, reported increases over 1996 in total numbers of reported cases. New York (1,264 cases), North Carolina (879), Virginia (690), and Maryland (619) reported the greatest numbers of cases [corrected]. Five states reported increases that exceeded 50%, compared with cases reported in 1996: Ohio (673.3%; 15 cases in 1996 to 116 in 1997). Massachusetts (144.3%; 115 to 281), South Carolina (97.9%; 96 to 190), Connecticut (97.4%; 274 to 541), and Maine (86.3%; 131 to 244). Cases of rabies associated with foci of rabies in foxes in west central Texas and in dogs and coyotes in southern Texas continued to decline, with this state reporting 78.3% fewer rabid foxes (13 cases), 26.7% fewer rabid dogs (11), and 63.2% fewer rabid coyotes (7) during 1997, compared with 1996. Reported cases of rabies in cats (300) and dogs (126) increased 12.8% and 13.5%, respectively, whereas cases in cattle (122) decreased by 6.9%. Thirty states, the District of Columbia, and Puerto Rico reported increases in rabies in animals during 1997, compared with decreases reported by 31 states and the District of Columbia in 1996. One state (Mississippi; 5 cases) remained unchanged. Hawaii was the only state that did not report a case of rabies in 1997. Four indigenously acquired cases of rabies reported in human beings were the result of infection with rabies virus variants associated with bats.

Causes, costs, and estimates of rabies postexposure prophylaxis treatments in the United States.

The incidence of rabies in humans in the United States is low. However, contacts with potentially rabid animals result in thousands of human rabies postexposure prophylaxis treatments (PEPs) each year. PEP is expensive, not without risk of adverse reactions, and in many instances unnecessary. Increased reports of cases of rabies in animals (4,880 cases in 1990, 9,495 in 1993, and 7,124 in 1996) suggested that PEPs could be increasing. Application of 1981 PEP incidence rates gave an estimate of approximately 16,000 PEPs during 1996, while calculations based on annual sales of a rabies biological during 1996 gave an estimate of approximately 39,000 PEPs. Appropriate usage of PEP requires careful evaluation of human exposure scenarios and adherence to approved guidelines.

Epidemiology of human rabies in the United States, 1980 to 1996.

PURPOSE: To summarize the epidemiologic, diagnostic, and clinical features of the 32 laboratory-confirmed cases of human rabies diagnosed in the United States from 1980 to 1996. DATA SOURCES: Data were obtained from case reports of human rabies submitted to the Centers for Disease Control and Prevention by state or local health authorities. STUDY SELECTION: All cases of human rabies reported in the United States from 1980 to 1996 in which infection with rabies virus was confirmed by laboratory studies. DATA EXTRACTION: Patients were reviewed for demographic characteristics, exposure history, rabies prophylaxis, clinical presentation, treatment, clinical course, diagnostic laboratory tests, identification of rabies virus variants, and the number of medical personnel or family members who required postexposure prophylaxis after coming in contact with an exposed person. DATA SYNTHESIS: 32 cases of human rabies were reported from 20 states. Patients ranged in age from 4 to 82 years and were predominantly male (63%). Most patients (25 of 32) had no definite history of an animal bite or other event associated with rabies virus transmission. Of the 32 cases, 17 (53%) were associated with rabies virus variants found in insectivorous bats, 12 (38%) with variants found in domestic dogs outside the United States, 2 (6%) with variants found in indigenous domestic dogs, and 1 (3%) with a variant found in indigenous skunks. Among the 7 patients with a definite exposure history, 6 cases were attributable to dog bites received in foreign countries and 1 was attributable to a bat bite received in the United States. In 12 of the 32 patients (38%), rabies was not clinically suspected and was diagnosed after death. In the remaining 20 cases (63%), the diagnosis of rabies was considered before death and samples were obtained specifically for laboratory confirmation a median of 7 days (range, 3 to 17 days) after the onset of clinical signs. Of the clinical differences between patients in whom rabies was diagnosed before death and those in whom it was diagnosed after death, the presence of hydrophobia or aerophobia was significantly associated with antemortem diagnosis (odds ratio, 11.0 [95% CI, 1.05 to 273.34]). The median number of medical personnel or familial contacts of the patients who received postexposure prophylaxis was 54 per patient (range, 4 to 179). None of the 32 patients with rabies received postexposure prophylaxis before the onset of clinical disease. CONCLUSIONS: In the United States, human rabies is rare but probably underdiagnosed. Rabies should be included in the differential diagnosis of any case of acute, rapidly progressing encephalitis, even if the patient does not recall being bitten by an animal. In addition to situations involving an animal bite, a scratch from an animal, or contact of mucous membranes with infectious saliva, postexposure prophylaxis should be considered if the history indicates that a bat was physically present, even if the person is unable to reliably report contact that could have resulted in a bite. Such a situation may arise when a bat bite causes an insignificant wound or the circumstances do not allow recognition of contact, such as when a bat is found in the room of a sleeping person or near a previously unattended child.

Rabies surveillance in the United States during 1996.

In 1996, 49 states, the District of Columbia, and Puerto Rico reported 7,124 cases of rabies in non-human animals and 4 cases in human beings to the Centers for Disease Control and Prevention. Nearly 92% (6,550 cases) were wild animals, whereas 8% (574 cases) were domestic species. The total number of reported cases decreased 9.6% from that of 1995 (7,881 cases). Although much of the decline was the result of fewer reported cases of rabies in raccoons, fewer cases were also reported among most groups of animals. Numbers of cases associated with separate epizootics of rabies in foxes in west central Texas and in dogs and coyotes in southern Texas attributable to canine variants have declined, with 56.2% fewer rabid foxes (60), 72.7% fewer rabid dogs (15), and 76.3% fewer rabid coyotes (19) during 1996, compared with cases of rabies reported among these same species during 1995. Nationally, the number of reported rabid bats (741) decreased 5.8%, with cases reported by 46 of the 48 contiguous states. Four Eastern Seaboard states, enzootic for the raccoon variant of the rabies virus, reported noteworthy increases in total numbers of reported cases: Maine (29.7%; 101 cases in 1995 to 131 in 1996), Maryland (44.2%; 441 to 636), North Carolina (59.0%; 466 to 741), and Virginia (33.3%; 459 to 612). Increases were also reported by Florida (6.4%; 251 to 267) and Georgia (3.1%; 294 to 303). Cats continued to be the domestic animal most frequently reported rabid, but reported cases of rabies in cats (266), cattle (131), and dogs (111) decreased by 7.6%, 3.7%, and 24.0%, respectively. Thirty-one states and the District of Columbia reported decreases in rabies in animals during 1996, compared with 18 states and Puerto Rico in 1995. Hawaii was the only state that did not report a case of rabies in 1996. Two indigenously acquired cases of rabies reported in human beings were the result of infection with rabies virus variants associated with bats, whereas the remaining 2 human rabies infections were acquired outside the United States, and the variants identified were consistent with those associated with rabid dogs.