Exposures of Novel H1N1 Influenza A Pandemic among Hospital Workers at a New York City (NYC) Tertiary Care Center

Background: Health care workers (HCWs) occupy a critical position during pandemics, being on the first line of exposure to infectious diseases and being responsible for mounting a care response. During the 2009 novel H1N1 influenza pandemic, all hospital staff including physicians at our medical center exposed to an ill patient, coworker or family member were required to report to Employee Health for consideration of antiviral prophylaxis.

Objective: To understand the rates and epidemiological curve of influenza exposures and surrounding circumstances at a NYC tertiary care center.

Methods: This retrospective study evaluated personnel health records of known influenza exposures between May 1, 2009 and February 28, 2010. Additional information regarding potential nosocomial exposures was obtained from Hospital Epidemiology. Exposures in the first (May 1- August 31, 2009) and second waves (September 1-February 28, 2010) of the pandemic were compared.  Descriptive statistics, Chi-square and Mann-Whitley tests were utilized.

Results: A total of 195 staff with known nosocomial exposure to influenza reported to Employee Health during the study period (58.4% in the first wave, and 40.6% in the second wave), of which 8 individuals had two separate exposures. The epidemiological curve of exposures was similar to rates of influenza-like illnesses (ILIs) among our staff, and to total NYC ILI ED visits (table 1).  About 76% of exposures occurred in hospital workers with high likelihood of patient contact (physicians 22%, nurses 42%, ancillary staff 17.4%), with no statistical difference seen in the type of staff presenting in the first and second wave (p =0.80). A majority (95%) of the known exposures reported were at work: patients represented 51.6 %, coworkers 37.6% and no data available for 10.8%.  Most of the reported exposures occurred on clinical wards (52%), followed by ICUs (18.4%), and ED (5%). Average time to presentation after exposure was 1.34 days (range 1-22). Antiviral prophylaxis was given to 70.7% of reporters (with exposures presenting within 2 days being most likely to receive prophylaxes (p <0.0005)). Only 4% reported concurrent symptoms and were tested for influenza.  Of 402 staff who presented with ILIs to Employee Health during the same season, 48 (12%) reported prior exposure at work, 17 of who tested positive for influenza.

Hospital Epidemiology identified 11 exposure episodes, ranging in size from 5 to 42.  Among these, 7 were due to coworker contacts and 4 represented patient contacts. On average, more exposures resulted from employee cases compared to patient cases (17.7 vs 10.5, p=0.285).

Conclusions: These data reveal the importance of early identification and isolation of sick hospital employees. The role of work place exposures in propagating the pandemic, especially earlier in the season, is highlighted.