Healthcare-Associated Infection Outbreak Investigations by the Centers for Disease Control and Prevention: 1946-2005

Background: Since its inception in 1946, Centers for Disease Control and Prevention (CDC) Epidemic Intelligence Service Officers (EISOs) have investigated outbreaks of healthcare-associated infections (HAI) and adverse events associated with delivery of health care.  These investigations often reflected problems that were unique, urgent, or difficult to control.

Objective: To review onsite HAI outbreak investigations carried out by CDC EISOs during 1946-2005 (study period) and highlight HAI risk factors ascertained during this period and their public health implications.

Methods: We reviewed CDC archived data on all onsite HAI outbreak investigations conducted by EISOs during the study period.  For each outbreak, we recorded the causative agent, location of occurrence, whether single or multiple institutions were involved, any epidemiologic linkage to specific risk factors (e.g., invasive devices, practices and procedures, contaminated products), recommendations, and interventions.

Results:  During the study period, EISOs conducted 531 outbreak investigations in U.S. facilities and abroad (33 facilities in 13 countries).  From 1946-1979, the majority (25%) of outbreaks involved gastrointestinal tract infections; however, by 2005, bloodstream (28%), surgical wound (18%), skin (15%), and respiratory tract (13%) infections predominated.  During 1946-1979, the predominant pathogens implicated in these outbreaks were Staphylococcus aureus (16%) and Salmonella spp. (10%).  By the end of the 1990s, other Gram-negative pathogens (27%), mycobacteria (11%), Enterococcus spp. (7%), or yeasts (5%) predominated, although various unusual organisms were often implicated. Outbreak types varied and were often linked to transfer of colonized patients or health care personnel between facilities (multihospital outbreaks), national distribution of contaminated products, use of invasive medical devices, variances in practices and procedures in health care environments (e.g., intensive care units, water reservoirs, or hemodialysis units), design flaws in medical products, common usage errors that encourage in-use contamination in hospitals, or laboratory errors (i.e., pseudooutbreaks).

Conclusions: Over the past six decades, CDC outbreak investigations have led to the characterization of HAIs, and identification of emerging pathogens and new modes of transmission.  Data from these investigations have contributed to CDC-generated publications or guidelines for prevention and control of HAI.  EISOs have met the challenges and complexities of outbreak investigations through a process of mentoring, on-the-job supervision and training, and systematic application of epidemiology, statistics, and laboratory science. Finally, through partnerships with health care facilities and local and state health departments, outbreaks have been terminated and lives saved.