Which factor increases the diagnostic yield of sputum cultures in suspected pneumonia?

• A. Collecting a sample after antibiotics started
• B. Collecting a deep cough sample early in the morning before antibiotics
• C. Collecting only saliva
• D. Collecting from a nonsterile container

Answer: (B)

The main idea is that the chance of identifying the pneumonia-causing organism from a sputum culture is highest when you obtain a true lower-respiratory sample before any antibiotics are started. A deep cough sample collected first thing in the morning tends to contain more sputum from the lower airways and less contamination from oral bacteria, so the lab is more likely to recover the pathogen. If antibiotics have already been started, their effect can reduce or eliminate viable bacteria, lowering the likelihood of a positive culture. Similarly, samples that are just saliva or collected in a nonsterile container are more contaminated with oral or environmental organisms, which makes it harder to pinpoint the actual pathogen.