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Approximately 500 children younger than 5 years old resident in 7 villages in a rural area of the Gambia were monitored closely for 1 year for episodes of acute lower respiratory tract infection (ALRI). Each episode was investigated with antigen detection techniques and antibody assays as well as culture for bacteria and viruses. A pathogen was identified in 76 (34.2) of 222 cases with clinical signs of ALRI and in 34 (42) of the 81 cases who, in addition, had radiologic evidence of ALRI. Evidence of infection with a bacterial pathogen, most commonly Streptococcus pneumoniaeor Haemophilus influenzae, was obtained in 32 (14.4) cases with clinical signs of ALRI (23.5 of those with radiologically proved pneumonia). Viral agents were cultured from 42 (19) of 221 cases but also from 14 (14.6) of 96 controls some of whom had minor symptoms of upper respiratory tract infection. In the absence of an outbreak of respiratory syncytial virus the viral agents recovered most often were influenza A and adenoviruses.

Seventy-four children ages 1 to 9 years hospitalized because of severe pneumonia were investigated using blood cultures, lung aspirates, nasopharyngeal aspirates, serology and antigen detection procedures. A bacterial infection was identified in 57 (77), a viral infection was seen in 25 (34) and 18 (24) had mixed viralbacterial infections. The bacterial pathogens most frequently identified were Streptococcus pneumoniaeand Haemophilus influenzaefound in 61 and 15 of patients, respectively. The viral pathogen most frequently recovered was respiratory syncytial virus (12). Evidence of Chlamydia pneumoniaestrain TWAR and Mycoplasma pneumoniaeinfection was found in 12 and 4 of cases, respectively. Overall a potential pathogen was identified in 60 (81) children, with evidence of polymicrobial infection in 30 cases (40.5). The study provides information on the relative role of different infectious agents in the etiology of severe pneumonia in children in a developing country.

Ninety infants less than 1 year of age with pneumonia and 43 control infants were investigated for viral and chlamydial infection with the use of culture and serology and for bacterial infection with the use of blood cultures, lung aspirates, antibody assays and antigen detection procedures. One or more potential pathogens were identified in 62 (69) cases with pneumonia and in 12 (28) controls. Infection by respiratory viruses was identified in 42 (49) cases and in 8 (19) controls. Respiratory syncytial virus was the commonest pathogen identified and was found in 32 cases (37). Bacterial infections were also common, being found in 27 (30) cases and 3 (7) controls, and predominantly involved Streptococcus pneumonias(20) or Haemophilus influenzae(11). Bacterial infections were associated with raised white blood cell counts and were identified more often by antigen detection procedures (68) than by culture of blood or lung aspirates (34) or by serology (33). Mixed viral-bacterial infections were identified in 13 cases (15). Infection with Chlamydia trachomatiswas diagnosed in 2 infants with acute lower respiratory tract infection and in 1 control infant.