Our study did not detect APM in a large collection of specimens from patients with pneumonia, which indicates that this virus is not a common cause of severe acute respiratory disease. Because APM is an ameba-associated pathogen like Legionella, exposures to APM are most likely to occur from environmental sources. Further studies of more epidemiologically appropriate populations may be necessary to adequately access the importance of APM as a potential human respiratory pathogen. The real-time PCR assays described here will help facilitate these studies.