Consensus statement ularemia, a bacterial zoono

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cisella tularensis grows best in cysteine- enriched broth and thioglycollate broth and on cysteine heart blood agar, buffered charcoal-yeast agar, and chocolate agar. Selective agar (such as chocolate agar selective for Neisseria gonorrhea isolation) may be useful when culturing materials from non- sterile sites, such as sputum. Inocu- lated media should be incubated at 37°C. Although growth may be visible as early as 24 to 48 hours after inocu- lation, growth may be delayed and cul- tures should be held for at least 10 days before discarding. Under ideal condi- tions, bacterial colonies on cysteine- enriched agar are typically 1 mm in diameter after 24 to 48 hours of incu- bation and 3 to 5 mm in diameter by 96 hours.60,81 On cysteine heart agar, F tularensis colonies are characteristi- cally opalescent and do not discolor the medium (FIGURE 4).

Antigen detection assays, polymer-

ase chain reaction, enzyme-linked im- munoassays, immunoblotting, pulsed- field gel electrophoresis, and other specialized techniques may be used to identify F tularensis and to characterize strains.84-87 These procedures are usu- ally performed only in research and ref- erence laboratories, however. In labora- tories where advanced methods are

established, results of antigen detection and polymerase chain reaction analyses can be obtained within several hours of receipt of isolates. Typically, serum an- tibody titers do not attain diagnostic lev- els until 10 or more days after onset of illness, and serology would provide mini- mal useful information for managing an outbreak. Serological confirmation of cases, however, may be of value for fo- rensic or epidemiological purposes. Most laboratories use tube agglutination or mi- croagglutination tests that detect com- bined immunoglobulin M and immu- noglobulin G.84,85 A 4-fold change in titer between acute and convalescent serum specimens, a single titer of at least 1:160 for tube agglutination or 1:128 for mi- croagglutination is diagnostic for F tu- larensis infection. Information on refer- ence diagnostic testing and shipping/ handling of specimens can be obtained from state public health laboratories and from the Division of Vector-Borne In- fectious Diseases, CDC, Fort Collins, Colo (telephone: [970] 221-6400; e-mail: [e-mail]).