As we move into the influenza and respiratory virus season, we anxiously anticipate the many patients with influenza-like-illness (ILI) who will be concerned that they have anthrax this year. Considering that children average three to six episodes of ILI (characterized by fever, fatigue, cough and other symptoms) per year and adults average one to three episodes per year, concern is not unwarranted. Please reassure your patients about the extremely low risk of anthrax in the absence of known history of exposure or occupational/environmental risk.

A combination of epidemiologic, clinical and, if indicated, laboratory and radiographic test results can help in evaluating persons in whom anthrax is a potential concern. For more extensive information about discerning the difference between ILI and anthrax, please see the November 9th, 2001 MMWR¹ . The following are highlights from that article:

Clinical Findings
Though details on the 11th case of inhalational anthrax are not known at this time, of the first ten cases of inhalational anthrax, only one had rhinorrhea, but all had fever/chills and fatigue/malaise, and eight had nausea or vomiting. Drenching sweats were a prominent symptom in 7 cases.

Testing
There is no rapid test to identify someone in the early stages of anthrax. Rapid tests for influenza are available, however they are characterized by low sensitivity (45% to 90%) and are highly dependent on specimen quality. Thus, a significant proportion of persons with influenza will be missed by these tests. In addition, studies have documented influenza infection in only about one-third of persons with ILI. None the less, rapid influenza testing in concert with viral culture on a subset of patients presenting with ILI may give you an idea of what influenza viruses are circulating and help you in diagnosing patients who visit your practice.

You can see which influenza viruses are currently circulating in King County on Public Health's website: (www.metrokc.gov/health/immunization/fluseason.htm). As of the week ending November 3rd, one case of influenza A, H1N1, has been reported in King County. In general, most cases of ILI are caused by viruses other than influenza (e.g. RSV, parainfluenza, adenovirus) and occasionally by bacteria (e.g. M. pneumoniae, C. pneumoniae).

All 10 of the initial inhalational anthrax cases had abnormal chest radiographs (CXR) on initial presentation; seven had mediastinal widening, seven had infiltrates and eight had plural effusion. CT scans were valuable in picking up these abnormalities and may show mediastinal lymphadenopathy before abnormalities are present on CXR. The high proportion of patients with pneumonia is a feature of anthrax associated with this bioterrorist attack that is different than what would be expected based on previous reports of naturally-occurring cases.

Blood cultures were positive in all seven of the inhalational anthrax patients who had not received antibiotics. Animal data suggests blood cultures may be positive relatively early in the course of illness.

Though not all persons with ILI should receive blood cultures, blood culture, along with a Gram's stain of a blood smear, chest radiograph (and possibly CT scan) should be considered in any patient with evidence of ILI and sepsis or ILI and a suspicious exposure or high-risk occupation.

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