Prevalence of infections caused by atypical pathogens in CAP

Physicians treating patients with community-acquired pneumonia tend to overestimate or underestimate the prevalence of infections caused by atypical pathogens. Are there any recent data that could be helpful in identifying patients with atypical infection?

Mark Woodhead: I would say first of all we should try to forget about atypical infections, particularly in patients who are not severely ill, because the evidence on the recent antibiotic trials – which show using a beta-lactam alone is as good as a beta-lactam plus a macrolide in these patients – suggest that adding in a macrolide is not adding anything.

We know historically that most infections caused by atypical bacteria are mild and generally self-limiting, so you may not need to use an antibiotic at all in such mild infections. For that reason, I do not think we should be too concerned about the infections caused by atypical organisms.

Recent studies – both recent antibiotic studies and studies using more sensitive methods for identifying organisms, such as molecular technologies – suggest that atypical pathogens are less common than we might have once thought, accounting for maybe 10% or less, or even as low as 2% of infections in some series. However, one note of caution about that is that we know that particularly, for example, mycoplasma pneumonia occurred in periodic waves or epidemics of infection, so occasional individual studies run the risk of missing times when there are more of such infections. But overall, as a general principle in patients who are not severely ill, we should not worry about atypical infections.