Diagnostic yields of different microbiological methods. Bars are percentages of cases with a positive test relative to the number of cases with a valid test, n (numbers inside the bars). Sputum culture: good-quality sputum by microscopy. A: Detection of bacteria and viruses, regardless of detection spectrum. B: Detection of S. pneumoniae and influenza viruses. OP, oropharynx; NP, nasopharynx; S. pneumoniae, Streptococcus pneumoniae; BAL, bronchoalveolar lavage; PCR, polymerase chain reaction.