Quantitative pathology of inhalational anthrax I: Quantitative microscopicfindings

Forty-one cases of documented inhalational anthrax from the Sverdlovsk epid emic of 1979 traced to release of aerosols of Bacillus anthracis at a secre t biologic-agent production facility were evaluated by semiquantitative his topathologic analysis of tissue concentrations of organisms, inflammation, hemorrhage, and other lesions in the mediastinum, mediastinal lymph nodes, bronchi, lungs, heart, spleen, liver, intestines, kidneys, adrenal glands, and central nervous system. These data were correlated with clinical, epide miologic, and demographic data. The patients' courses, with a variable incubation period and short nonspeci fic course (4 days before hospitalization) with rapid demise (1 day of hosp italization before death), correlated with systemic bacterial infection and lesions. Bacilllus anthracis were identified in all cases in which there w as no antibiotic treatment or there was treatment for fewer than 21 hours. The lesions that were the most severe and apparently of longest duration we re in the mediastinal lymph nodes and mediastinum. There and elsewhere, per ipheral transudate surrounded fibrin-rich edema; necrosis of arteries and v eins was the most likely source of large hemorrhages displacing tissue or i nfiltrating tissue, respectively; and apoptosis of lymphocytes was observed . Respiratory function was compromised by mediastinal expansion, large pleu ral effusions, and hematogenous and retrograde lymphatic vessel spread of B . anthracis to the lung with consequent pneumonia The central nervous syste m and intestines manifested similar hematogenous spread, vasculitis, hemorr hages, and edema These pathologic findings are consistent with previous exp erimental studies showing transport of inhaled spores to mediastinal lymph nodes, where germination and growth lead to local lesions and systemic spre ad, with resulting edema and cell death, owing to the effects of edema toxi n and lethal toxin. The identification of the vascular lesions as a basis f or the prominent hemorrhages is a novel observation for human inhalational anthrax.