Preventing transmission of 2009 H1N1 influenza within the healthcare setting: lessons learned from exposure events

Background: Preventing transmission of 2009 H1N1 influenza (nH1N1) within the healthcare setting has been a major focus of infection control (IC) programs in the wake of the pandemic.  Hierarchies of control include elimination of potential exposures, engineering controls, administrative controls, and personal protective equipment (PPE).  Study of factors leading to exposure can inform future measures for prevention of transmission of droplet-borne infections.   

Objective: To analyze the extent and cause of documented exposures to nH1N1 occurring at one U.S. medical center during the early part of the pandemic. 

Methods:

During the study period, all individuals with unprotected close contact with a probable or confirmed case of nH1N1 were identified by IC personnel, entered into an electronic database, and referred for further evaluation.  Data were analyzed to determine the number and role of individuals affected by exposure, clinical areas affected by exposures, and the apparent cause of the exposure. 

Results:

From April 29^th to August 31^st 2009, 1218 individuals had unprotected exposure to nH1N1 at our institution; including, 1168 healthcare workers (HCW) (96%), 46 patients, and 4 visitors.  Over this same period, a total of 239 cases of probable or confirmed nH1N1 influenza were cared for (49 inpatients, 190 outpatients or emergency department (ED)).  A total of 47 exposure events occurred; the median number of individuals exposed per event was 9, the range 0 to 138.  The majority of exposures occurred in the ED (33%), the general medicine floors (21%), or the intensive care units (16%).  Among HCW, the job types most likely to be exposed included: nurses (42% of exposures), physicians (18%), respiratory therapists (8%), and radiology technicians (7%).  While the median duration of exposure was 1 day, the range was < 1 to 9 days.  Infected patients were the source of 36 exposure events (77%), while infected HCW were the source in 11 (23%).  The total number of individuals exposed by an infected patient was 1012 (70%) vs. 206 (30%) exposed by a HCW.  The median size of exposure events caused by patients and HCW was similar (9.5 vs. 8 individuals exposed, respectively).  In 43 exposure events, IC documentation indicated a likely explanation for the exposure:  22 were due to a delay in initiation of isolation; 9 were due to a HCW working while ill; 5 were due to late clinical recognition of influenza; 4 were due to failure to implement precautions appropriately; 3 were due to inaccurate test results. 

Conclusions:

The burden of potential exposures to nH1N1 during the early part of the pandemic was high, particularly as many of these individuals were offered chemoprophylaxis during this timeframe.  This evaluation reveals a failure of several IC hierarchies, which can inform prevention efforts targeted to the clinical areas and HCW roles most likely to be affected by influenza exposures.