MYCOPLASMAL PNEUMONIA : CLINICAL ASPECTS
A mild tracheobronchitis with fever, cough, headache, and malaise is the most common syndrome associated with acute M. pneumoniae infection. The pneumonia is typically less severe than other bacterial pneumonias. It has been described as “walking” pneumonia, be-cause most cases do not require hospitalization. The disease is of insidious onset, with fever, headache, and malaise for 2 to 4 days before the onset of respiratory symptoms. Pul-monary symptoms are generally limited to a non- or minimally productive cough. X-rays reveal a unilateral or patchy pneumonia, usually in a lower lobe, although multiple lobes are sometimes involved. Small pleural effusions are seen in up to 25% of cases.
Pharyngitis with fever and sore throat may also occur. Nonpurulent otitis media or myringitis occurs concomitantly in approximately 15% of patients with M. pneumoniaepneumonitis. The presence of nonpurulent otitis media and lower respiratory illness in a teenager suggests M. pneumoniae infection.
Clinical diagnosis of M. pneumoniae infection may be difficult because the manifestations overlap with those of bacterial and viral infections. Gram-stained sputum usually shows some mononuclear cells, but, because it lacks a cell wall, M. pneumoniae is not seen. The absence of organisms, however, may help to suggest the etiology. The organism can be iso-lated from throat swabs or sputum of infected patients using special culture media and methods, but because of its slow growth, isolation usually requires incubation for a week or longer. Thus, serologic tests rather than cultures are more commonly used for specific diagnosis. A fourfold rise of serum antibody titer in acute and convalescent sera indicates M. pneumoniae infection. The most widely used serologic method is complement fixation.With the relatively long incubation period and insidious onset of the disease, many patients already have high antibody titers at the time they are first seen. In these situations, a single high titer, such as a complement fixation titer greater than 1:128 or IgM-specific antibody (measured by enzyme immunoassay or immunofluorescence), indicates recent or current infection, because these antibodies are generally of short duration.
Because more than two thirds of patients with symptomatic lower respiratory M. pneu-moniae infection develop high titers of cold hemagglutinins, their demonstration can beuseful in some clinical situations. It must be remembered that cold hemagglutinins are nonspecific and have been observed in adenovirus infections, infectious mononucleosis, and some other illnesses. The test is simple, however, and can be performed rapidly in any clinical laboratory. Direct detection of the organism in respiratory secretions has been attempted using immunoassay methods, DNA hybridization, and the polymerase chain re-action. These methods are not yet available for routine diagnosis.
Erythromycin or tetracycline are the usual agents used for treatment of M. pneumoniae infections. They shorten the course of infection, although eradication from the nasophar-ynx may take much longer. Azithromycin and clarithromycin are comparable to eryth-romycin, but clindamycin is not effective. Most quinolones are also active.