Identifying the cause of community-acquired pneumonia is more difficult in children than in adults for a variety of reasons. Procedures used to confirm the diagnosis, such as bronchoalveolar lavage and lung puncture for culture, are invasive and typically reserved for use in patients with complicated pneumonia. Acute and convalescent antibody titers generally are not available until the acute illness resolves. Little is known about the accuracy of serum antibody titers in confirming the diagnosis in association with cultures, polymerase chain reaction (PCR) testing, clinical course and therapy. Wubbel and associates compared the results of culture, PCR testing and serum antibody titers before and after antibiotic therapy in otherwise healthy children diagnosed with community-acquired pneumonia.

Otherwise healthy children between the ages of six months and 16 years who presented to the emergency department with tachypnea, fever, cough or rales and an abnormal chest radiograph were eligible for the study. Patients were randomized to one of two treatment groups. Those in the first group received azithromycin suspension, 10 mg per kg (maximum: 500 mg per day) on the first day, followed by 5 mg per kg (maximum: 250 mg per day) daily for the next four days. Those in the second group received a 10-day course of either amoxicillin-clavulanate potassium, in a dosage of 40 mg per kg per day in three divided doses if they were younger than five years, or erythromycin estolate suspension, in a dosage of 40 mg per kg per day (maximum: 1,500 mg per day) in three divided doses if they were older than five years.

Patients were evaluated at baseline and periodically over the next 37 days. Initial testing included blood cultures, nasopharyngeal swabs for Chlamydia pneumoniae and Mycoplasma pneumoniae culture and PCR, nasopharyngeal swab for viral direct fluorescent antibody (DFA) testing, and culture and acute serum antibody titers for these bacteria and Streptococcus pneumoniae. Follow-up swabs and blood cultures were obtained two to five weeks after therapy was initiated. A clinical response was defined as cure (complete resolution of signs and symptoms), improvement (incomplete resolution of signs and symptoms) or failure. A control group consisting of healthy children attending a well-child clinic was selected to match study patients for nasopharyngeal and pharyngeal swabs for cultures and PCR testing.

A total of 168 children were included in the study. In 73 (43 percent), an etiology for their pneumonia was identified. The measurement of antibody response in paired sera was the best means of identifying infections caused by M. pneumoniae (10 of 12 patients) or C. pneumoniae (10 of 10 patients). Culture and PCR testing were less effective in identifying etiologies. A total of 129 patients were evaluated for acute and convalescent serologic responses to S. pneumoniae. Of these, 35 (27 percent) had evidence of acute pneumococcal infection. A total of 143 patients were considered cured following therapy; however, there was no difference in effectiveness among therapies. Viral agents, most commonly respiratory syncytial virus, influenza A and parainfluenza 3, were the principal organisms present in nasopharyngeal secretions of children younger than eight years.

The authors conclude that measuring antibody response in paired sera remains the most accurate means of identifying the etiology of pneumonia in ambulatory children. Chest radiographs, blood cultures or total white blood cell counts and differential counts are not effective in differentiating etiologic agents. There was no difference in effectiveness of the antibiotics used in the study, even among children for whom the cause of pneumonia was identified. Therefore, the choice of antimicrobial agent for the treatment of these children should continue to be based on clinical judgment.

editor's note: Several risk factors increase the severity of pneumonia in children, including prematurity, malnutrition, low socioeconomic status, passive exposure to tobacco smoke and exposure to other children at a day-care center. Radiographic testing is considered the gold standard because clinical findings do not consistently identify true cases of pneumonia. However, the absence of respiratory distress, tachypnea, crackles and decreased breath sounds accurately excludes pneumonia with a high specificity. The principal management issue concerns distinguishing bacterial infections from viral infections, because antibiotics are not effective in treating the latter. Advances in diagnostic testing that help physicians distinguish between the two will be very useful.—r.s.