October 5, 2007

Beware of misidentification of Francisella tularensis as Actinobacillus or Hemophilus species and the risk of aerosols in the Clinical Laboratory

The causative agents of tularemia include Francisella tularensis subspecies tularensis and Francisella tularensis subspecies holarctica. In the event of a natural outbreak of tularemia or a bioterrorism attack clinicians should be aware of potential misidentification of these organisms by clinical laboratories.

The CDC/ASM/APHL “Basic Protocols for Level A Laboratories for the presumptive identification of Francisella tularensis” posted at: http://emergency.cdc.gov/agent/tularemia/ emphasizes that:

A. ‘The most common misidentification of F. tularensis is Haemophilus influenza and Actinobacillus species’.

B. “Identification of isolates by using commercial identification systems is not recommended due to the high probability of misidentification. The Vitek NHI panel may give as high as 99% confidence to the identification of Actinobacillus actinomycetemcomitans with strains of F. tularensis”.

C. Another important reason that commercial identification systems should not be used to identify Francisella tularensis is because of the “potential of generating aerosols” that could put laboratory workers at risk for one or more of the multiple tularemia clinical syndromes.

Given the rarity of Actinobacillus infections in most US hospitals, if a commercial identification system was used then consideration of a misidentification of F. tularensis should be considered if the patient’s clinical presentation is consistent with tularemia.

In the clinically unlikely event of a “cluster” of Actinobacillus isolates involving more than one patient, then a coordinated evaluation of the patients and their bacterial laboratory isolates, by both clinicians and laboratorians, should be completed rapidly to rule out tularemia.

Daniel R. Lucey MD, MPH

Director, Center for Biologic Counterterrorism and Emerging Diseases

EROne Institute, Dept of Emergency Medicine, Washington Hospital Center

Adjunct Professor Microbiology and Immunology

Georgetown University Medical Center, Washington, DC

Website for this posting: www.BePast.org

E-mail: Daniel.R.Lucey@Medstar.net

E-mail #2: drl23@georgetown.edu