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Am Fam Physician. 2004;69(5):1227-1228

Community-acquired respiratory viruses (CRVs) cause most of the acute lower respiratory infections in children that result in hospitalization. These viruses, most common in fall, winter, and early spring, include influenza virus, respiratory syncytial virus, parainfluenza virus, adenovirus, coronavirus, and rhinovirus. Cell culture isolation from respiratory secretions is the standard for diagnosis of respiratory virus infections and requires two to 10 days to complete. Rapid diagnostic procedures, frequently using direct immunofluorescence assay (DFA) or membrane enzyme-linked immunosorbent assay are becoming widely available; they detect respiratory viral antigens within 10 to 60 minutes. The sensitivity of these assays is 70 to 95 percent. Shetty and associates studied the efficacy of the DFA technique in detecting common viruses in nasopharyngeal samples and assessed the clinical usefulness of concomitant conventional viral cultures.

Nasopharyngeal samples from 1,670 children hospitalized for management of lower respiratory tract infection were tested for CRVs by DFA and culture. Children with chronic lung disorders, congenital heart disease, or immunocompromise were excluded. The impact of viral culture and DFA test results on management was measured by the amount of time required to recognize positive results, the length of the hospital stay, and the effect of test results on antibiotic therapy and duration of hospitalization decisions.

Of the 1,557 evaluable samples, virus was detected by either DFA or culture in 468 (30 percent). The study included 140 children with a mean age of 8.6 months who had culture-proven lower respiratory tract infection. Bronchiolitis was the most common diagnosis, followed by pneumonia and croup. Antibiotics were started empirically in 102 patients (73 percent) but were stopped within 48 hours of admission in 49 patients (48 percent), based on a positive DFA or negative bacterial culture. Because the mean hospital stay was 3.6 days and the mean time for viral cultures to become positive was 7.7 days, most viral culture results were not available before discharge. The results of the viral cultures did not affect treatment or hospital discharge date in any patient.

The authors conclude that viral cultures are not useful in otherwise healthy children hospitalized for community-acquired lower respiratory tract infections. Antibiotic decisions were made on the basis of rapid viral antigen testing using DFA and, although false-positive antigen did occur, viral culture results were not available until after discharge and did not affect any clinical decisions.

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