Antibiotic Prophylaxis After Tick Bites
The clinically relevant spectrum of tickborne disease includes Lyme disease, ehrlichiosis, babesiosis, and viral encephalitis. Clinicians, patients, and interested parties have concern about what to do in the face of a tick bite. Cases of Lyme disease in the state of Maryland are outnumbered by patients presenting with concerns about a tick bite by more than 10 to 1.
Three main choices are available to clinicians presented with a patient recently bitten by a tick: 1) immediate treatment with antibiotics, 2) observation and treatment if symptoms develop, 3) baseline and 3-6 weeks serologic testing, with treatment initiated on the basis of serologic or clinical manifestations.
In support of option #1 is a cost-effectiveness analysis examining prevention of Lyme disease after tick bite, which concluded that if probability of infection was 3.6% or greater, empiric treatment is indicated and that, even if probability is 1.0-3.5%, treatment may be preferred. This information may be coupled with a meta-analysis which indicated that the average rate of infection in untreated victims of black-legged ticks in endemic areas was 1.0-3.4%. Unfortunately, the authors point out that using amoxicillin treatment, as an example, for every case of Lyme disease prevented, not only would eight patients like incur a drug-related rash, one patient would be anticipated to sustain a severe or life-threatening reaction.
Option #2 results in cost savings as a result of minimizing unnecessary treatment costs and costs of adverse reactions. Although 60-80% of persons infected develop a characteristic rash, at which point treatments almost always produce complete cure, theoretical concerns address the possibility that some individuals will develop subclinical infection which, untreated, could evolve into difficult, and costly, sequelae. To date, this concern has not been observed to occur.
Option #3 has limitations of inadequacies of current serological tests, as well as costs of testing.
The authors conclude that prophylaxis of tick bites to prevent lime disease should not yet be recommended, except in those circumstances where duration of an identified tick attachment may help identify a high risk group.
Dennis DT. Lancet 1997;350:1191-1192.
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