Usefulness of Gram stain for diagnosis of lower respiratory tract infection or urinary tract infection and as an aid in guiding treatment.

During a prospective study of 8 months duration conducted in the Department of Internal Medicine and the Department of Pulmonary Diseases of the Academic Medical Centre, Amsterdam, Gram stainings of sputa and urine were performed for all patients whose clinical symptoms indicated an acute urinary tract infection or pulmonary infection. On the test request, the physician reported which antibiotic treatment he would prescribe if a microscopic examination was not available. The results of the Gram stain were discussed by the microbiologist with the physician, and the antibiotic therapy recommended by the microbiologist was recorded. This recommendation was compared with the antibiotic prescription noted in the patient record 1 day later. Two days after the results of final cultures and susceptibility tests became available, the patient record was again investigated for changes in the antibiotic regimen. Of 57 urine samples and 103 sputa, 27 and 85, respectively, were derived from patients with an infection of the urinary tract or respiratory tract. The results of the Gram stain confirmed the physician's suspicion 91% of the time for urinary tract infections and 81% of the time for pulmonary infections. In 67% of the patients with suspected lower respiratory tract infections and in 58% of patients with suspected urinary tract infections, the antibiotic treatment recommended on the basis of the results of the Gram stain differed significantly from the antibiotic treatment that the physician would have prescribed had a microscopic examination not been performed. The microbiologist's advice on antibiotic treatment was followed in 79% of the cases of respiratory tract infection and in 65% of the cases of urinary tract infection. The antibiotic treatment was adjusted to the final results of culture and antimicrobial susceptibility testing in 54% of the urinary tract infections and in 31% of the respiratory tract infections. The results indicate that the examination of sputa and urine in patients suspected to have an infection of the respiratory tract or urinary tract influences the antibiotic choice considerably.