VAIL, COLO. – The differential diagnosis of pediatric infectious disease emergencies marked by fever and rash can quickly be narrowed by paying close attention to the type of rash.
Infectious diseases featuring fever and rash that require emergency diagnosis and treatment include fever with rashes that are purpuric, petechial, or erythrodermic, Dr. Marsha S. Anderson said at a conference on pediatric infectious diseases sponsored by the Children’s Hospital Colorado.
Fever with purpura
Heading the list of diagnostic possibilities here is meningococcemia, which she called "every pediatrician’s nightmare" because of a case-fatality rate of 10%-20% even with appropriate treatment.
Complicating the situation is the fact that in a minority of cases the rash is petechial rather than purpuric.
"This is a disease that deserves your respect. Just remember: With fever and purpura, or fever and petechiae, meningococcemia needs to be at the top of your differential," stressed Dr. Anderson, a pediatric infectious diseases specialist at the University of Colorado.
The attack rate is highest in infants and young children because they haven’t yet experienced the transient nasopharyngeal colonization by Neisseria species that permits formation of protective strain-specific antibodies, she explained.
Empiric therapy until the diagnostic lab work and drug susceptibilities become available is vancomycin plus ceftriaxone. This combination also covers the other serious infectious causes of pediatric fever and purpura: Haemophilus influenzae, Streptococcus pneumoniae, and Staphylococcus aureus.
Once Neisseria meningitidis has been isolated, the antibiotic therapy can be narrowed to penicillin, cefotaxime, or ceftriaxone. The recommended treatment duration is 7 days for uncomplicated meningococcemia or meningococcal meningitis.
S. pneumoniae causes fever and purpura fulminans mainly in children who are immunocompromised.
Fever with petechiae
"Rocky Mountain spotted fever is another diagnosis you really don’t want to miss. You want to make this diagnosis and institute therapy promptly. Many studies have shown decreased mortality if doxycycline is initiated in the first 5 days of illness," Dr. Anderson said.
That can be a challenge. The distinctive petechial rash, which begins on the hands, wrists, feet, and ankles, and then moves centrally, typically doesn’t show up until day 5 or 6. In one study of 92 patients admitted with an ultimate diagnosis of Rocky Mountain spotted fever, the rash on admission was maculopapular rather than petechial in about one-third of cases (J. Pediatr. 2007;150:180-4).
Fever, myalgias, and headache are common at the onset of the illness, which is typically 2-14 days after a tick bite involving transmission of Rickettsia rickettsii. The diagnosis must be made clinically as there is no rapid testing commercially available. Demonstration of a fourfold antibody titer rise between acute and convalescent serology can confirm the diagnosis. Only about one-half of confirmed cases feature patient recall of a tick bite, so absence of such a history shouldn’t allay suspicion that this disease is present.
Doxycycline is the first-line agent used for treatment of Rocky Mountain spotted fever in children of all ages. The usual length of doxycycline therapy is 7-14 days, or for at least several days after the patient is afebrile and clinically improved. In a patient with a life-threatening allergy to doxycycline, chloramphenicol is an alternative. Availability of chloramphenicol, especially in the oral formulation, may be limited in the United States.
Other serious infections involving fever and petechiae include meningococcemia, group A streptococcal infection, rat bite fever, ehrlichiosis, and anaplasmosis. Unlike Rocky Mountain spotted fever, where a petechial or maculopapular rash occurs in 90% of cases, only about 10% of patients with ehrlichiosis or anaplasmosis develop a rash.
Rat bite fever is an acute febrile illness caused by Streptobacillus moniliformis, which colonizes the nasopharynx of a substantial percentage of domestic and wild rats. Children can develop the illness by kissing their pet rat or letting it eat food from their mouth.
Most cases of rat bite fever resolve spontaneously within 2 weeks; however, the case-fatality rate is 13% without treatment, which is penicillin or doxycycline.
Fever with erythroderma, a sunburnlike rash
The differential diagnosis here consists of toxic shock syndrome, staphylococcal scalded skin, and Kawasaki disease. Drug reactions, including Stevens-Johnson syndrome, are an important noninfectious cause. Sulfa drugs, anticonvulsants, and NSAIDs are the drugs most commonly associated with Stevens-Johnson syndrome.
Suspect toxic shock syndrome when fever and erythroderma are accompanied by hypotension, red eyes and lips, and a strawberry tongue. These are patients who warrant transfer to an intensive care unit. A key treatment principle is to search out the source of infection and drain it, whether it is a paronychia, sinusitis, perirectal abscess, or some other focus. If tampons are present they should be removed. Many experts use vancomycin and clindamycin as empiric therapy to treat toxic shock syndrome. Toxic shock syndrome results in vascular leakage, so fluid resuscitation and support of vascular volume are vital.