Failure to respond is usually evident by day 3 of therapy.
Causes of nonresponse to initial therapy:
(1) inadequate antimicrobial therapy
(2) pathogen resistant to initial antibiotic regimen
(3) wrong diagnosis (not healthcare-associated pneumonia, see below)
(4) empyema or lung abscess
(5) drug fever or drug reaction
(6) Clostridium difficile disease
(7) occult extrapulmonary infection (sinusitis, abscess, other)
Pulmonary conditions that may mimic HAP:
(1) atelectasis
(2) pulmonary embolism
(3) ARDS
(4) pulmonary hemorrhage
(5) neoplasm
