Atypical Pneumonia Diagnosis

More recent studies have further confused the diagnostic picture, raising many more questions about the utility of the designation "atypical pneumonia." In a study from Israel by Lieberman and associates (12), 346 patients were seen. The vast majority of diagnostic tests were serologic, and multiple causative agents were found in 133 (38.4%) of the patients. The second most frequent infection was caused by the organism M pneumoniae.

Infections due to multiple agents are common. Does this matter? Moreover, does it make any difference at all which agent is involved in cases of community-acquired pneumonia? How M pneumoniae infection and perhaps, to an even greater extent, C pneumoniae infection may predispose a patient to a second infection is easily seen by their pathologic effect on ciliated epithelium. Both infectious agents cause ciliostasis, which makes the host more susceptible to infection by other, more virulent pathogens such as S pneumoniae.

Atypical Pneumonia Treatment

It is interesting that in another report by Lieberman and associates, two thirds of patients who had a coinfection with M pneumoniae had a severity of illness that was not different from those patients in whom the sole pathogen recognized was M pneumoniae. Whether patients infected with more than one pathogen need to be approached differently than those with a single pathogen is largely academic, however. Treatment decisions should always be made empirically because no reliable clues may be obtained at the time of diagnosis.

Gram's stain, although time-honored, has never been validated, and a recent meta-analysis clearly casts some doubt on its usefulness in guiding therapy. This view, however, is not shared by some investigators, as the recent community-acquired pneumonia guidelines by the Infectious Diseases Society of America would imply (18). In my opinion, Gram's stain is not sufficiently helpful and probably should not be relied on when deciding whether to limit broad-spectrum therapy. Until rapid diagnostic tests using molecular techniques become available, treatment of community-acquired pneumonia should be chosen empirically on the basis of clinical and radiographic presentations.

In this situation, therapy has to be defined by severity of illness. Young patients who have no serious comorbid conditions and whose clinical condition does not warrant hospitalization can be safely treated as outpatients either with a newer macrolide or with doxycycline.

Once a patient is hospitalized because of the severity of illness and the presence of multiple comorbid conditions, however, it must be decided which of the infections needs treatment. Clearly, those due to S pneumoniae must be treated. In addition, appropriate therapy for infections due to L pneumophila is needed to dissipate further worry about pneumonia caused by Mycoplasma and Chlamydia organisms.

Just how to treat these patients also depends on whether beta-lactam-resistant S pneumoniae is present in the individual community. With the ever-increasing incidence of such organisms, the time-honored combination of a beta lactam plus a macrolide is probably going to give way to the use of respiratory fluoroquinolones (20). At present, the latter therapy makes the most sense in hospitalized patients.