Diagnosis of acute respiratory tract infections: serology and new methods.

No test is available that can identify all potential pathogens in acute respiratory tract infections. Each diagnostic test is associated with limitations with respect to sensitivity and/or specificity and/or speed, and thus a combination of tests has to be used. Even so, no etiologic agent is found in 30--60% of cases. The following methods are recommended for use in the routine laboratory for the diagnosis of infections: (1) Legionella --- direct immunofluorescence test, culture, serology and antigen detection (available only in specialized laboratories); (2) Chlamydia pneumoniae --- micro-immunofluorescence test, complement fixation, but not direct antigen detection by immunofluorescence; (3) Mycoplasma pneumoniae - complement fixation and/or particle agglutination or other evaluated methods; (4) Coxiella burnetii --- immunofluorescence test (IgG and IgM) and complement fixation; (5) viruses --- complement fixation or other similar test (ELISAs often lack adequate evaluation). Culture for Chlamydia, Mycoplasma pneumoniae, Coxiella burnetii and viruses should only be performed by very experienced laboratories. Most procedures deliver results only retrospectively or too late. The most promising diagnostic tools for the future are nucleic acid amplification techniques (NAT) or PCR, which could solve many of the problems connected with conventional techniques, but there are enormous contamination problems. Further research and worldwide aid in the development of standardized NAT, especially by industrial companies, is urgently encouraged to improve the laboratory diagnosis of these pneumonias.