Rocky Mountain Spotted Fever: Clinical, Laboratory, and Epidemiological Features of 262 Cases

Abstract

Most previous reports of Rocky Mountain spotted fever (RMSF) have included cases either not laboratory confirmed or confirmed by relatively weak diagnostic criteria. In the present study detailed epidemiological, clinical, and laboratory features of 262 confirmed or highly probable cases of RMSF reported from six states from 1977 to 1980 were analyzed. This analysis revealed that early clinical diagnosis of RMSF is difficult because the illness may have a gradual or an abrupt onset, the symptoms and signs may be unusual in timing or frequency, and the clinical appearance may vary depending on such factors as age and location of residence. RMSF was diagnosed later in those who died than in survivors, primarily because of atypical initial symptoms and the late onset of rash. RMSF should be considered in any individual who, during the spring and summer, has been in RMSF-endemic areas and develops a fever, regardless of the absence of rash or history of tick exposure.

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

“…Tickborne rickettsial diseases continue to cause severe illness and death in otherwise healthy adults and children, despite the availability of effective antibacterial therapy. Early signs and symptoms of tickborne rickettsial illnesses are nonspecific, and most cases of RMSF are misdiagnosed at the patient's first visit for medical care, even in areas where awareness of RMSF is high (6,7). To increase the likelihood of an early, accurate diagnosis, health care providers should be familiar with risk factors, signs, and symptoms consistent with tickborne rickettsial diseases.…”

“…A rash typically appears 2-4 days after the onset of fever; however, most patients initially seek health care before appearance of a rash (25,74,98). The classic triad of fever, rash, and reported tick bite is present in only a minority of patients during initial presentation to health care (6,25); therefore, health care providers should not wait for development of this triad before considering a diagnosis of RMSF.…”

“…The classic spotted or generalized petechial rash, including involvement of the palms and soles, usually appears by day 5 or 6 and is indicative of advanced disease. Absence of rash should not preclude consideration of RMSF; <50% of patients have a rash in the first 3 days of illness, and a smaller percentage of patients never develop a rash (6,25). The rash might be atypical, localized, faint, or evanescent (99).…”

Comparison of Immunofluorescence, Western Blotting, and Cross-Adsorption Assays for Diagnosis of African Tick Bite Fever

“…Several tests are available, but with the exception of immunofluorescence assay (IFA), Western blotting (WB), and cross-adsorption assay, most are not recommended (10, 11). IFA, which can detect immunoglobulin G (IgG) and IgM antibodies, has a sensitivity rate ranging from 84 to 100% (1,6,13,15). Poor species specificity is a major drawback, but this may be circumvented by using a multiple-antigen IFA where reactions to several species can be compared directly (4, 13).…”

“…The present report constitutes one of the few serological evaluations of consecutive patients with rickettsioses. In contrast to most previous studies, which are retrospective and based on clinical samples submitted to reference laboratories (1,6,13,15), our series of patients contains many cases with uncomplicated and mild presentation (e.g., not necessitating antibiotic therapy or hospitalization). With a sensitivity rate of only 45%, the present data indicate that IFA, the considered reference method in rickettsial infections (10) and a commercially available test used by laboratories worldwide, may miss many cases of ATBF.…”