Diagnostic value of Gram stain and culture of sputum and endotracheal aspirates in bacteremic pneumococcal pneumonia

Value of intensive diagnostic microbiological investigation in low- and high-risk patients with community-acquired pneumonia

In a prospective study to evaluate the diagnostic yield of different microbiological tests in hospitalised patients with community-acquired pneumonia, material for microbiological investigation was obtained from 262 patients. Clinical samples consisted of the following: sputum for Gram staining, culture, and detection of pneumococcal antigen; blood for culture and serological tests; urine for detection of Legionella pneumophila serogroup 1 antigen and pneumococcal antigen; and specimens obtained by fiberoptic bronchoscopy. A pathogen was identified in 158 (60%) patients, with Streptococcus pneumoniae (n=97) being the most common causative agent of community-acquired pneumonia. In 82% of the 44 patients with an adequate sputum specimen, a positive Gram stain was confirmed by positive sputum culture. S. pneumoniae infections were detected principally when adequate sputum specimens were examined by Gram stain and culture and when adequate and inadequate sputum specimens were tested for the presence of pneumococcal antigen (n=58; 60%). The urinary pneumococcal antigen test was the most valuable single test for detection of S. pneumoniae infections (n=52; 54%) when sputum pneumococcal antigen determination was not performed. Fiberoptic bronchoscopy was of additive diagnostic value in 49% of the patients who did not expectorate sputum and in 52% of those in whom treatment failed. Investigation of sputum by a combination of Gram stain, culture, and detection of pneumococcal antigen was the most useful means of establishing an aetiological diagnosis of community-acquired pneumonia, followed by testing of urine for pneumococcal antigen. Fiberoptic bronchoscopy may be of additional value when treatment failure occurs.

Effect of sputum induction by hypertonic saline on specimen quality

Microbiologic work-up of expectorated material is routinely used to search for the etiology of pulmonary infections, but sputum is often contaminated by saliva. Inhalation of hypertonic saline induces bronchial secretions and theoretically may improve specimen quality. We compared in a laboratory-blinded, randomized study the quality of sputum obtained either with induction by saline or without induction in patients with respiratory tract infection and a history of productive cough. The quality of sputum was considered good if the polymorphonuclear neutrophils (PMNs)/squamous epithelial cells (SECs) ratio was > or = 2 or the Q (quality) score was > or = +1 on Gram stain. Forty-nine and 50 patients were able to expectorate in the induced and spontaneous sputum groups, respectively. PMNs/SECs ratio was > or = 2 in 65% and 74% of the patients in the induced and spontaneous sputum groups (p = 0.47); for the Q score, a value > or = +1 was found in 55% and 66% of the patients of each group (p = 0.37). In conclusion, sputum induction by hypertonic saline inhalation does not improve specimen quality as judged by the PMNs/SECs ratio on Gram stain.