Differential Diagnosis: Since naturally occurring outbreaks of Q fever are reported, an outbreak from a terror source could be difficult to distinguish from a natural one. Further, the protean manifestations require differentiation from diseases ranging from a wide variety of diseases. The acute febrile illness would need to be distinguished from influenza and dengue as well as the prodrome of a variety of bacterial or viral illnesses. The rounded densities evident on chest radiograph call to mind Legionnaire's disease and tularemia. Other causes of atypical pneumonia such as Mycoplasma pneumoniae, Legionella pneumophila, Chlamydia psittaci, and Chlamydia pneumoniae as well as agents such as Yersinia pestis associated with rapidly progressive pneumonia should also be considered. Acute hepatitis would need to be differentiated from the usual causes of hepatitis (e.g., A, B, and C). Likewise, the occasional case that presents with primary meningitis/encephalitis would need to be differentiated from the usual viral causes of aseptic meningitis/encephalitis and occasionally form agents associated with pleocytic CSF with a mononuclear predominance-listeriosis, leptospirosis, lymphocytic choriomeningitis, tuberculosis, and Rocky Mountain spotted fever.
Diagnostic Tests: A fourfold rise in IgG titer between acute and convalescent serum samples drawn > 14 days apart or a single specimen with IgM antibody (seen as early as 10-14 days into illness) is diagnostic of Q fever. Antibody to C. burnetii may be demonstrated by indirect fluorescent antibody (IFA), enzyme-linked immunosorbent assay (ELISA), and complement fixation (relatively insensitive). Isolation is impractical as the organism is rarely found in sputum, is difficult to culture, and is a significant hazard to laboratory personnel.
Specimen Submission: Specimens should not be submitted for isolation. Serum specimens must be triple contained in an approved shipping container and have biohazard labels. Before transport is arranged the receiving laboratory must be alerted prior to transport by calling (800) 252-8239 ("press 1"). Newly available diagnostic tests may be discussed at that time. Specimens must be accompanied by a Specimen Submission Form and submitted to the Texas Department of State Health Services Laboratory, 1100 West 49th Street, Austin, TX 78756.
Additional Tests: Chest x-ray abnormalities may be seen in just over half of patients. Nonsegmental and segmental pleural-based opacities are common. Rounded opacities and hilar adenopathy are not uncommon. Small pleural effusions may be seen in about 35% of cases. There may be mild elevation (2-3 times the normal) of hepatic transaminase levels. Although serum bilirubin is usually normal, jaundice may occur. The white blood cell count is increased in one-third of patients. C. burnetii has been isolated from the cerebrospinal fluid of patients with central nervous system infection, suggested by fever and severe headache; however, cerebrospinal fluid is usually normal.