Managing potential laboratory exposures to Francisella tularensis
Francisella tularensis is highly infectious when grown in culture, and laboratory-acquired infections have been documented. The isolation of F. tularensis from clinical specimens, especially if unanticipated, can generate concern among laboratory workers about possible exposure.
Management options for potentially exposed workers include a “fever watch” or antimicrobial prophylaxis. During a fever watch, workers monitor their temperature with instructions to seek immediate treatment for tularemia if they develop a fever (usually defined as a single oral temperature above 101 °F or 38.5 °C).
There are no set criteria for determining who should be managed by fever watch and who would benefit from immediate prophylaxis. Factors to consider when making this decision include:
- Nature of the exposure — Workers who report sniffing a culture plate or conducting procedures that generate aerosols are probably at greater risk than those who simply worked with the organism on the bench.
- Incubation period — The typical incubation period for tularemia is 3–7 days (range 1–14 days). Much of this period may have passed by the time the organism is positively identified, in which case, the remaining risk of infection is low.
- Level of concern — Some laboratory workers may be very anxious regarding their risk of infection, while others may be more concerned about taking medications unnecessarily.
Doxycycline (100 mg orally BID X 14 days) is generally recommended for prophylaxis in adults. Ciprofloxacin (500 mg orally BID) is not FDA-approved for prophylaxis of tularemia but has demonstrated efficacy in various studies, and may be an alternative for patients unable to take doxycycline.