Rocky Mountain Spotted Fever in the United States, 2000–2007: Interpreting Contemporary Increases in Incidence

Abstract

Abstract. Rocky Mountain spotted fever (RMSF), a potentially fatal tick-borne infection caused by Rickettsia rickettsii , is considered a notifiable condition in the United States. During 2000 to 2007, the annual reported incidence of RMSF increased from 1.7 to 7 cases per million persons from 2000 to 2007, the highest rate ever recorded. American Indians had a significantly higher incidence than other race groups. Children 5-9 years of age appeared at highest risk for fatal outcome. Enzyme-linked immunosorbent assays became more widely available beginning in 2004 and were used to diagnose 38% of cases during [2005][2006][2007]. The proportion of cases classified as confirmed RMSF decreased from 15% in 2000 to 4% in 2007. Concomitantly, case fatality decreased from 2.2% to 0.3%. The decreasing proportion of confirmed cases and cases with fatal outcome suggests that changes in diagnostic and surveillance practices may be influencing the observed increase in reported incidence rates.

Zoonotic Infections Among Employees from Great Smoky Mountains and Rocky Mountain National Parks, 2008–2009

“…Incident infections with spotted fever group rickettsiae were noted in both parks. GRSM runs though Tennessee and North Carolina, which are among the top states for the reported incidence of RMSF (Openshaw et al 2010). While a focus of unusually severe and fatal RMSF has been noted in western Tennessee, a milder focus has been identified in North Carolina, fueling speculation that some RMSF reports in this state may actually reflect less pathogenic spotted fever group rickettsiae circulating in the area, such as R. parkeri or R. amblyomii (Apperson et al 2008;Adjemian et al 2009).…”

“…GRSM is the most visited U.S. national park, averaging 10 million visitors per year and employing > 300 permanent staff. It spans parts of Tennessee and North Carolina, states which report the greatest numbers of Rocky Mountain spotted fever (RMSF) cases (Adjemian et al 2009;Openshaw et al 2010). ROMO also receives millions of visitors each year, and maintains > 230 permanent staff.…”

Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis — United States

“…SFG rickettsiosis, ehrlichiosis, and anaplasmosis are nationally notifiable in the United States. Cases have been reported in each month of the year, although most cases are reported during April-September, coincident with peak levels of tick host-seeking activity (3)(4)(5)(9)(10)(11)(12)(13)(14). The distribution of tickborne rickettsial diseases varies geographically in the United States and approximates the primary tick vector distributions, making it important for health care providers to be familiar with the regions where tickborne rickettsial diseases are common.…”

Assessment of Real-Time PCR Assay for Detection of Rickettsia spp. and Rickettsia rickettsii in Banked Clinical Samples

“…Symptoms of this disease may include, but are not limited to, high fever, headache, and rash, with the potential for a fatal outcome (1). National case fatality rates are Ͻ1% but can approach 7% in some regions to which it is highly endemic; a fatal outcome may be averted with timely administration of doxycycline (2,3).…”

“…However, serologic tests are frequently negative during the acute phase of illness, and currently available molecular tests are not reliable for use in patient management when applied to acute-phase blood samples, which may have very few organisms (3,4). Clinical management of suspected RMSF cases based on test results is not recommended, partly because of diagnostic assay limitations, and physicians must treat suspected cases empirically (4).…”