Table 1.

Overview of Microbiological Investigations Performed on Samples and Diagnostic Criteria

Specimen	Infectious agent	Assay	Diagnostic criteria
BAL fluid	Aerobic bacteria	Culture	≥104 cfu/mL (cut-off value)
	Viruses	Culture	Growth
	Respiratory virusesa	Multiplex PCR	Positive
	Atypicalb	Multiplex PCR	Positive
NPA	Viruses	Culture	Growth
	Respiratory virusesa	Multiplex PCR	Positive
	Atypicalb	Multiplex PCR	Positive
Blood	Aerobic bacteria	Culture	Growth
	Virusesc	Complement fixation	Acute titer ≥120d or 4-fold increase
	Mycoplasma pneumoniae	Complement fixation	Acute titer ≥320d or 4-fold increase
Pleural fluid	Bacteria	Culture	Growth

NOTE. BAL, bronchoalveolar lavage; cfu, colony-forming units; NPA, nasopharyngeal aspirate; PCR, polymerase chain reaction.

^aInfluenzavirus A and B; parainfluenza virus types 1, 2, 3; respiratory syncytial virus; human metapneumovirus subtypes A and B; coronavirus 229E and OC43.

^b M. pneumoniae and Chlamydophila pneumoniae.

^cSerological testing for influenzavirus A and B, adenovirus, picornavirus, and respiratory syncytial virus.

^dReverse titer.