Consensus statement ularemia, a bacterial zoono

DIAGNOSIS

Tularemia in humans occurs infre- quently, resulting in a low index of di- agnostic suspicion among clinicians and laboratorians. Since rapid diagnostic testing for tularemia is not widely avail- able, the first indication of intentional tularemia might follow recognition by public health authorities of a cluster- ing of acute, severe respiratory illness with unusual epidemiological fea- tures (Table 1). Suspicion of tulare- mia might be triggered in alert clini-

cians encountering patients with findings of atypical pneumonia, pleu- ritis, and hilar lymphadenopathy. Iden- tification of F tularensis in clinical speci- mens may be missed or delayed for days or weeks when procedures for routine microbiological screening of bacterial pathogens are followed, and it is un- likely that a serendipitous laboratory identification would be the sentinel event that alerted authorities to a ma- jor bioterrorism action.

Physicians who suspect inhala-

tional tularemia should promptly col- lect specimens of respiratory secre- tions and blood and alert the laboratory to the need for special diagnostic and safety procedures. Francisella tularen- sis may be identified by direct exami- nation of secretions, exudates, or bi- opsy specimens using direct fluorescent antibody or immunohistochemical stains.81-83 By light microscopy, the organism is characterized by its small size (0.2µm× 0.2-0.7 µm), pleomor- phism, and faint staining. It does not show the bipolar staining characteris- tics of Yersinia pestis,4 the agent of plague, and is easily distinguished from the large gram-positive rods character- istic of vegetative forms of Bacillus anthracis (FIGURE 3).2 Microscopic demonstration of F tularensis using fluorescent-labeled antibodies is a rapid diagnostic procedure performed in des- ignated reference laboratories in the Na- tional Public Health Laboratory Net- work; test results can be made available within several hours of receiving the ap- propriate specimens if the laboratory is alerted and prepared. Suspicion of in- halational tularemia must be promptly reported to local or state public health authorities so timely epidemiological and environmental investigations can be made (BOX).

Growth of F tularensis in culture is

the definitive means of confirming the diagnosis of tularemia.60,81 Francisella tularensis can be grown from pharyn- geal washings, sputum specimens, and even fasting gastric aspirates in a high proportion of patients with inhala- tional tularemia.56 It is only occasion- ally isolated from the blood. Fran-

Figure 2. Chest Radiograph of a Patient With Pulmonary Tularemia

Infiltrates in left lower lung, tenting of diaphragm, prob- ably caused by pleural effusion, and enlargement of left hilum. Source: Armed Forces Institute of Pathology.