Types of situations that may lead to a pseudo-outbreak in a health care facility:
(1) problem in clinical diagnosis
(2) problem in laboratory diagnosis
(3) change in surveillance (improved efficiency, better reporting, etc.)
(4) random chance resulting in a clustering of cases unrelated to nosocomial spread
Problems in clinical diagnosis:
(1) misdiagnosis of the clinical condition, including use of wrong data (dirty surgical case classified as clean, etc.)
(2) misinterpretation of culture isolates showing colonization as infection
(3) misclassification of a community-acquired infection as a nosocomial infection
Problems in laboratory diagnosis:
(1) contamination in specimen collection
(2) contamination during transportation
(3) contamination during processing
(4) contamination of cultures and/or or testing system (PCR, etc.)
(5) misidentification of isolate or misinterpreting results (inadequate methods for isolate identification, reading a mixed culture, new methodology, etc.)
(6) ultrasensitive but nonspecific methodology
