Researchers have identified some early signs of inhalation anthrax that should make distinguishing it from other acute respiratory infections easier. For example, mediastinal widening and pleural effusions evident on chest X-ray are sensitive and specific indications of inhalation anthrax. Vomiting, cyanosis, and mental status changes are also more common with inhalation anthrax than with other acute respiratory infections.

Researchers studied 36 cases of naturally occurring inhalation anthrax reported between 1880 and 1976 and 11 cases from the bioterrorism attacks in 2001. Finding few differences between the two groups, researchers combined them into one group of 47 cases. They then compared each case in that group with four cases each of community-acquired pneumonia and influenza-like illness.

Of the 22 people with inhalation anthrax who had a chest X-ray, 100% had a widened mediastinum, pleural effusion, or both. These findings were present in only 28% of pneumonia cases and 4% of flulike cases. About 63% of people with anthrax had syncope and confusion or coma, compared with less than 1% of those with pneumonia and none of those with influenza-like symptoms.

The study authors write that nausea, vomiting, pallor or cyanosis, diaphoresis, altered mental status, and raised hematocrit level seem to predict inhalation anthrax. They say that caregivers should be suspicious if more than one patient has these signs and symptoms; because inhalation anthrax is rare in nature, a cluster of cases suggests bioterrorism.

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