O'Brien KL, et al. - Via a multi-site, international case-control study in nine study sites in seven countries (Bangladesh, The Gambia, Kenya, Mali, South Africa, Thailand, and Zambia) on 4,232 children aged 1-59 months who were admitted to hospital with severe pneumonia, experts evaluated causes of pneumonia in young African and Asian children, using unique analytical methods implemented to clinical and microbiological findings. Out of 1,752 cases recruited for primary analysis, wheezing was present in 555 cases. Positive blood culture was observed in 56 out of 1,749 cases; Streptococcus pneumoniae was the most common bacteria isolated. At least one pathogen discovered by PCR in the nasopharyngeal and oropharyngeal specimens was found in almost all cases and controls. In comparison to severe cases, bacteria was more common than viruses in very severe pneumonia. The main ten pathogens of each site accounted for 79% or more of the site's etiological fraction. For most cases of pneumonia needing hospital admission, a small set of pathogens were to blame. Furthermore, the prevention and treatment of such a subset of pathogens could substantially alter childhood pneumonia outcomes.