Diagnostic Value of Microscopic Examination of Gram-Stained Sputum and Sputum Cultures in Patients with Bacteremic Pneumococcal Pneumonia

Abstract

Clinicians continue to question the usefulness of microscopic examination of Gram-stained sputum specimens ("Gram staining") and sputum culture for diagnosis of pneumonia. We analyzed the sensitivity of these techniques in 105 patients with pneumococcal pneumonia proven by blood culture. Gram staining revealed gram-positive cocci in pairs and chains, and culture yielded pneumococci in only 31% and 44% of all cases, respectively. However, sputum specimens were never submitted for examination in 31 cases; in 16 others, the specimen was inadequate and a culture was not done. Excluding these cases, the sensitivities of Gram staining and culture were 57% and 79%, respectively. If patients receiving antibiotics for >24 h had been excluded, Gram staining would have suggested pneumococci in 63%, and culture results would have been positive in 86%. Sensitivity increased in inverse proportion to the duration of antibiotic therapy (P<.05). Microscopic examination of sputum samples before antibiotics were administered and performance of culture within 24 h of receipt of such treatment yielded the correct diagnosis in >80% of cases of pneumococcal pneumonia.

Improving the use of sputum cultures in lower respiratory tract infection

“…14 Other studies have shown that the quality of sampling improves after an educational intervention similar to the one used in our study, 6 and that diagnostic yield for S. pneumoniae can potentially increase substantially with improvement in sputum quality. 15 In general our findings are supportive of literature showing that sputum samples have little overall impact upon practical management of patients. [2][3][4]16,17 Prior to our intervention approximately 13% of sputum samples (45/347) appeared to lead to a change in management, but half of these samples were 'inappropriate'.…”

Impact of infant 13-valent pneumococcal conjugate vaccine on serotypes in adult pneumonia

“…Adults with a positive BinaxNOW test, Bio-Plex test or blood culture for S. pneumoniae were deemed to have pneumococcal CAP. Respiratory samples were not used for the diagnosis of pneumococcal disease or determination of pneumococcal serotype in this study, due to the poor sensitivity and specificity reported in previous studies [12,13].…”

Randomised controlled trial and health economic evaluation of the impact of diagnostic testing for influenza, respiratory syncytial virus and Streptococcus pneumoniae infection on the management of acute admissions in the elderly and high-risk 18- to 64-year-olds

“…119 In our study, sputum culture had a sensitivity of 100% (2.5-100%) (see Chapter 5) when compared with blood culture as the reference standard but the CIs were extremely wide due to the infrequency of a productive cough in our cohort. Musher et al 120 analysed 105 patients with pneumococcal pneumonia proven by blood culture -sputum culture was positive in only 44% of all cases. These investigators reviewed earlier articles and noted that sensitivity of Gram staining in proven cases of pneumococcal pneumonia ranged from 20% to 69% and that the sensitivity of culture ranged from 29% to 94% (see Chapter 6).…”

“…The CIs are wide due to the small number of patients with a positive blood culture and productive cough. Musher et al 120 analysed 105 patients with pneumococcal pneumonia proven by blood culture. Sputum culture yielded a pneumococcus in 44% of cases.…”

“…Sensitivity data for sputum culture from that review and several recent studies are shown in Table 25. 119,120,[162][163][164][165][166][167] Random-effects meta-analysis of the data in Table 25 reveals sensitivities of 43% (33-53.0%) when cases who received antibiotics are included, and 59% (21-92%) when they are excluded. Specificity data are not available, but the specificity of sputum culture is generally poor due to colonisation of the respiratory tract.…”