Vol. 20, No. 40
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER
Tuesday, October 2, 2001
A. Provided by Leslie Edwards Reger, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene.
No information available.
B. The Johns Hopkins Hospital, Department of Pathology. Information provided by Anil V. Parwani, M.D., Ph.D.
Case Report
A 7-year-old white male presented to the emergency room after 5 days
of fever. In the prior 24 hours he had episode of emesis and a rash appeared
on his arms, legs, chest, abdomen and shoulders. He was treated with amoxicillin
for a presumed otitis media since day 2 of the fever. On physical exam
he appeared ill and had an oral temperature of 38.8 C, pulse rate of 110/min
and respiratory rate of 20/minute. Admission labs reveal a serum sodium
of 128 mEq/L, BUN 1.8 mg/dL, AST 58 U/L. ALT 60 U/L, serum albumin 1.6
g/dL, WBC of 4.6/mm3 (55% neutrophils, 25% bands, 15% lymphocytes
and 5% monocytes), platelets of 84,000/mm3. He rapidly deteriorated
with hypotension, facial edema, enlarging hemorrhagic and purpuric skin
lesions, increasing dyspnea and confusion. Chest x-ray revealed a pattern
consistent with pulmonary edema. The patient was transferred to intensive
care for careful hemodynamic monitoring. All cultures were negative. A
skin biopsy for the detection of R. rickettsii antigen was positive.
A diagnosis of rocky mountain spotted fever was made.
Rocky Mountain Spotted Fever (RMSF)
Organism and Clinical spectrum: Rocky mountain spotted fever is a common and often severe rickettsial illness. The disease is caused by Rickettsia rickettsii which are spread by ixodid ticks. The Rickettsia species are members of the family Ricketsiaceae. They are small bacteria that live intracellularly (endothelial cells). Initial signs and symptoms of RMSF can be nonspecific and may include sudden onset of fever, headaches, and rash. Later signs include rash, abdominal pain, joint pain, nausea, vomiting and diarrhea. The characteristic RMSF rash (petechial) may not occur until day 6 or later of the infection and may only occur in 85% of the patients. The disease is often difficult to diagnose in the early stages and in the absence of appropriate treatment may be fatal (3-5% fatality rate). Long term sequelae may include partial paralysis, hearing loss, incontinence, movement and language disorders.
Natural History and Epidemiology: Ticks are the natural hosts
and serve as vectors and reservoirs of R. rickettsii. There are
two major vectors of R. rickettsii in the United States, the American
dog tick (Dermacentor variabilis) and the Rocky Mountain wood tick
(Dermacentor andersoni). Both male and female ticks will bite. The
rickettsial organisms are transmitted to the vertebrate host via saliva
during a tick bite. The ticks have four stages in their life cycle, egg,
larva, nymph and adult. After the eggs hatch, each stage must feed once
to go to the next stage.
Epidemiology: The majority of the RMSF cases occur from April to September. The annual number of cases reported to CDC varies from 250 to 1200. The cumulative number of 2001 cases reported by CDC up to the week ending September 22, 2001 was 380. Over half the number of RMSF cases are reported from the south Atlantic region. Other parts of the United States such as the Pacific and west south central states have also reported RMSF cases. The highest number of cases are usually in North Carolina. Over two-thirds of the cases occur in children less than 15 years of age. Individuals residing in the vicinity of wooded areas or high grass may have increased rate of infection.
Diagnosis: Treatment decisions regarding RMSF should be made immediately on clinical suspicions and should never be delayed while waiting for laboratory confirmation. Serologic assays are widely available and are used by most reference laboratories but often nonreactive during acute illness. An indirect immunofluorescent antibody method is used to detect either IgG or IgM antibodies. Increased IgM titers may be seen after 1 week of infection. Skin biopsy of the rash followed by immunostaining for R. rickettsii antigens is diagnostic in 70% of patients with RMSF.
Treatment: Treatment of choice for RMSF in adults and children is doxycycline and should be started immediately on the basis of clinical suspicion. If the treatment is initiated with 4-5 days after infection, fever usually subsidizes 24 to 72 hours after initiation of treatment.
References: