Diagnosis of Legionnaires' disease. An update of laboratory methods with new emphasis on isolation by culture
J. J. Zuravleff, V. L. Yu, J. W. Shonnard, B. K. Davis and J. D. Rihs
A prospective clinical study of 40 cases of legionnaires' disease combined
with serial laboratory examinations enabled us to present an update as well
as new recommendations concerning the use of diagnostic tests for
legionnaires' disease. Transtracheal aspirate specimens are the optimal
specimen for recovery of Legionella pneumophila by culture as well as the
most sensitive method for early diagnosis. In addition, with recent
improvements in culture media and methodology, L pneumophila can now be
readily isolated from sputum. Examination of respiratory specimens by
direct immunofluorescence (DFA) is useful, but the sensitivity is much less
than that of culture. The yield from DFA examination directly correlates
with the number of L pneumophila recoverable by cultural methods; thus, the
DFA test result may be negative in an early or mild case of legionnaires'
disease. Antibody titers were elevated in 27% of cases within one week of
onset of pneumonia and may, therefore, be useful in early diagnosis in
selected patients.
