28 July 2008

Disease due to F. tularensis “Fx1” Infection

The clinical history of a patient with a microbiological= ly atypical Francisella tularensis infection, termed “Fx1”, was presented in a microbiology journal by co-authors from Texas and Umea, Sweden over a decade ago. As part of a new series on this we= bsite of patients and clinical syndromes of past of particular interest, this patient’s clinical course is summarized below.

The patient was a 55 year-old man who lived in Galveston, Texas on a beachfront cottage. He h= ad diabetes and had been on prednisone, 20mg each day for an unstated duration, “for inflammatory nodular skin lesions of unknown etiology”. The severity and treatment of his diabetes was also unstated. He was hospitaliz= ed in June 1991 with a three week history of weakness, shortness of breath on exertion, chest pain, and restfulness.&nbs= p; He was found to have diffuse wheezing in = both lungs and moderate enlargement of his liver and spleen. On his third day in= the hospital he developed a high fever (39.8 C), headache, and an increased peripheral white blood cell count.

Work-up revealed two positive blood cultures obtained wi= th his fever that grew a Francisella species termed “Fx1”. An MRI brain scan was interpreted as showing brain abscesses with a maximum size of 12mm. The initial spinal flui= d exam culture was not commented on, but there were 25 white blood cells (92% of w= hich were mononuclear cells), an elevated protein of 107 mg/dl and a glucose of 84mg/dl (without a peripheral blood glucose being reported and thus unable = to be interpreted as within normal limits or not).

A chest X-ray after the fever appeared revealed “n= ew pleura-based infiltrates in the right lower lung”. No sputum was produced. Extensive testing that included an echocardiogram, an EEG, and a 4-vessel cerebral angiogram was negative. The patient was treated with “expanded-spectrum cephalosporins”. Subsequently, both his fever and his right lower lung abnormality resolved. No information was provided on any further brain imaging or longer-term clinical follow-up. His presumptive diagnosis was bacteremia, pneumonia, and brain abscesses due to the “Fx1” bacteria.

Serologic testing for Francisella was negative when performed two weeks after the positive blood culture. The patient lived with a “tick-infested dog”, but no results of testing for Fx1 infectio= n of the dog, the ticks, or any other potential environmental sources were presented.

The two positive blood cultures grew a small, gram-negative coccoid bacteria (“termed “Fx1̶= 1;) in the aerobic bottle after three days using the BACTEC blood culture syste= m. Importantly, the Vitek NHI panel suggested an (incorrect) identification of= the Fx1 Francisella bacteria as Hemophilus Actinomycetemcomitans with a 99% confidence level (see page 1998 under the “Growth and biochemical results” section of this paper). . While this “Fx1” bacte= rium was susceptible in vitro to ceftriaxone, ciprofloxacin, imipenem and chloramphenicol, it was resistant to penicillin, ampicillin, amoxicillin-cl= avulanate, aztreonam, cephalothin, and trimethoprim-sulfamethoxazole.

This patient is the only one published, to this writer’s knowledge, with infection due to this Fx1 Francisella bacter= ia (in subsequent years further identified as Francisella tularensis novicida = (or “novicida-like”).

The importance of mis-identification of this bacteria as Hemophilus Actinomycetemcomitans (with 99% confidence level by Vitek NHI panel), should be emphasized in the event of an environmental contamination= with Francisella “Fx1”. In such a situation, explicit public health = and medical recommendations must be made to perform surveillance and testing of= any clinical specimens (e.g., blood, skin, sputum, pleural fluid, lung, spinal fluid, or brain) from ill patients who could have been exposed to this cont= aminated environment who have Hemophilus Actinomycetemcomitans bacteria identified in the clinical laboratory, given that the true identity of such bacteria could well be an atypical Francisella tularensis species such as Fx1.<= /span>

Daniel R. Lucey MD, MPH

EROne Institutes, Department of Emergency Medicine<= /o:p>

Was= hington Hospital Center=

Adjunct Professor of Microbiology and Immunology

Geo= rgetown University Medical<= /st1:PlaceName> Center=

Was= hington, D.C.

Website for this posting: www.BePast.org

e-mail: DRL23@Georgetown.edu

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