Sporadic Legionnaires' disease. A pathologic study of 23 fatal cases.

Twenty-three fatal sporadic cases of serogroup 1 Legionella pneumophila pneumonia have been analyzed. Bilateral consolidating fibrinopurulent pneumonia was evident in most cases. In four leukopenic immunosuppressed subjects, and acute fibrinoserous pneumonia with a remarkable lack on inflammation was present. The bacterium was found at extrathoracic sites in 27% of the cases. Involvement of the spleen (25%), bone marrow (13%), and kidneys (4.5%) suggests that hematogenous spread of the infection is not uncommon. Involvement of the hilar lymph nodes in 44% of the cases, and multiple peripheral lymph nodes in one case, suggest that lymphatic vessels may also be an important pathway of dissemination. We concluded that systemic spread of L pneumophila is not uncommon in seriously ill patients and we believe that some of the unusual extrathoracic manifestations of this disease may be related to bacteremia.