Incidence Of Rocky Mountain Spotted Fever Research Articles

735 - Trends in rocky mountain spotted fever incidence in Oklahoma 2007–2016

735 - Trends in rocky mountain spotted fever incidence in Oklahoma 2007–2016

A forty-year review of Rocky Mountain spotted fever cases in California shows clinical and epidemiologic changes.

Rocky Mountain spotted fever (RMSF) is a life-threatening tick-borne disease documented in North, Central, and South America. In California, RMSF is rare; nonetheless, recent fatal cases highlight ecological cycles of the two genera of ticks, Dermacentor and Rhipicephalus, known to transmit the disease. These ticks occur in completely different habitats (sylvatic and peridomestic, respectively) resulting in different exposure risks for humans. This study summarizes the demographic, exposure, and clinical aspects associated with the last 40 years of reported RMSF cases to the California Department of Public Health (CDPH). Seventy-eight RMSF cases with onsets from 1980 to 2019 were reviewed. The incidence of RMSF has risen in the last 20 years from 0.04 cases per million to 0.07 cases per million (a two-fold increase in reports), though the percentage of cases that were confirmed dropped significantly from 72% to 25% of all reported cases. Notably, Hispanic/Latino populations saw the greatest rise in incidence. Cases of RMSF in California result from autochthonous and out-of-state exposures. During the last 20 years, more cases reported exposure in Southern California or Mexico than in the previous 20 years. The driver of these epidemiologic changes is likely the establishment and expansion of Rhipicephalus sanguineus sensu lato ticks in Southern California and on-going outbreaks of RMSF in northern Mexico. Analysis of available electronically reported clinical data from 2011 to 2019 showed that 57% of reported cases presented with serious illness requiring hospitalization with a 7% mortality. The difficulty in recognizing RMSF is due to a non-specific clinical presentation; however, querying patients on the potential of tick exposure in both sylvatic and peridomestic environments may facilitate appropriate testing and treatment.

Hierarchical Bayesian Spatio-Temporal Analysis of Climatic and Socio-Economic Determinants of Rocky Mountain Spotted Fever.

This study aims to examine the spatio-temporal dynamics of Rocky Mountain spotted fever (RMSF) prevalence in four contiguous states of Midwestern United States, and to determine the impact of environmental and socio–economic factors associated with this disease. Bayesian hierarchical models were used to quantify space and time only trends and spatio–temporal interaction effect in the case reports submitted to the state health departments in the region. Various socio–economic, environmental and climatic covariates screened a priori in a bivariate procedure were added to a main–effects Bayesian model in progressive steps to evaluate important drivers of RMSF space-time patterns in the region. Our results show a steady increase in RMSF incidence over the study period to newer geographic areas, and the posterior probabilities of county-specific trends indicate clustering of high risk counties in the central and southern parts of the study region. At the spatial scale of a county, the prevalence levels of RMSF is influenced by poverty status, average relative humidity, and average land surface temperature (>35°C) in the region, and the relevance of these factors in the context of climate–change impacts on tick–borne diseases are discussed.

Prevalence of Seropositivity to Spotted Fever Group Rickettsiae and Anaplasma phagocytophilum in a Large, Demographically Diverse US Sample

Most epidemiologic studies of tick-borne rickettsial diseases in the United States are small and have limited demographic scope, making broader risk assessment difficult. We conducted a seroprevalence study of spotted fever group rickettsiae and Anaplasma phagocytophilum, the agent of human granulocytic anaplasmosis. Specimens were selected randomly from the Department of Defense Serum Repository for 10,000 diverse military personnel at various stages in their careers who were serving with active duty status in 1997. Antibody testing included enzyme-linked immunosorbent assay for Rickettsia rickettsii and A. phagocytophilum, and Western blot confirmation for A. phagocytophilum. Risk factors were assessed using logistic regression. Subjects were mostly male and young and were diverse ethnically and geographically. Spotted fever group rickettsiae seropositivity was 6.0% (95% confidence interval, 5.5%-6.4%). In univariable logistic regression, seroprevalence was significantly higher among older subjects, men (6.5%, compared with 3.3% among women), black individuals (8.7%, compared with 5.6% among white individuals), subjects from states with above-average Rocky Mountain spotted fever incidence, and subjects in ground combat specialties. Associations remained significant in multivariable analysis for age, sex, black versus white race, home state with high incidence, and ground combat specialty. Among 696 subjects with serum samples obtained within 7 days after entering the military, the rate of seropositivity was 3.4% (95% confidence interval, 2.1%-4.8%). Seroprevalence was nonsignificantly lower in men (3.4%, compared with 3.7% in women ) and in black individuals (3.4%, compared with 4.1% in white individuals). A. phagocytophilum seropositivity, as determined by by enzyme-linked immunosorbent assay and Western blot, was 2.6% and 0.11% (95% confidence interval, 0.05%-0.18%), respectively. Western blot seropositivity was not significantly associated with subject characteristics in univariable analysis. Spotted fever group rickettsiae exposure was common and A. phagocytophilum exposure was rare in a US population with broad demographic diversity.

Rocky Mountain spotted fever in Clermont County, Ohio. II. Distribution of population and infected ticks in an endemic area.

The epidemiology of Rocky Mountain spotted fever (RMSF) in relation to the distribution of the human population and infected ticks has not been defined. A study was undertaken in Clermont County, Ohio, to describe the distribution of population in a highly endemic focus of RMSF and to determine the prevalence of ticks infected with rickettsiae of the spotted fever group. This area was compared to another area of similar size in the same county where the incidence of RMSF was much lower. The population in the highly endemic area was distributed diffusely throughout the area, allowing maximum interfacing of the human population and the tick vector. The population distribution in the other area differed from the endemic area in that most of the population was concentrated in one town. Of 1168 Dermacentor variabilis collected in the endemic area, 18 (1.5%) were infected, compared to four (1.2%) of 339 ticks in the other area. Past studies of infected ticks have not identified the specific strains or species of spotted fever group rickettsiae. In this study, 11 rickettsiae were serotyped by microimmunofluorescence. Four were Rickettsia rickettsii, five were R. montana, and two were unclassified rickettsiae of the spotted fever group.