Quantification of Nasopharyngeai Bacteria for Diagnosis of Respiratory Tract Infection in Children

Abstract

Agreement between clinical signs of bacterial respiratory tract infections and quantities of respiratory tract pathogens in nasopharynx was studied in 77 children, aged 6–13 years. Specimens were obtained from 27 clinically bacterial and 51 clinically non-bacterial respiratory tract infections, and in 124 instances from healthy children. Viable counts of Streptococcus pneumoniae, Haemophilus influenzae, Branhamella catarrhalis, and beta-haemolytic streptococci were made from swab specimens suspended in saline before being plated on agar media. The frequency of these species in children with clinically bacterial, non-bacterial and no signs of respiratory tract infections were 85%, 47% and 26%, respectively. Bacterial counts >10⁴ colony-forming units (CFU)/ml of the pathogens occurred in 59% of clinically bacterial infections, as compared with 18% in clinically non-bacterial infections (p<0.001), the corresponding figures for counts >10³ CFU/ml being 85% and 41% (p<0.01), respectively. At neither level of bacterial count (i.e. >10⁴ or >10³), was there a significant difference between the healthy and those with a clinically non-bacterial infection. The quantification of bacteria in nasopharyngeal samples may thus be of clinical diagnostic value.