Eleven HCP had probable or possible acquisition in the community, and two had no reported exposures in either health-care or community settings. Among 11 HCP with probable or possible patient to HCP acquisition and available information on PPE use, only three reported always using either a surgical mask or an N95 respirator. These findings suggest that transmission of novel influenza A (H1N1) virus to HCP is occurring in both health-care and community settings and that additional messages aimed at reinforcing current infection-control recommendations are needed.

After identifying the first two cases of novel influenza A (H1N1) infection in the United States on April 15, 2009, CDC requested that all state and local health departments implement enhanced surveillance for unsubtypable influenza A viruses (3). On May 4, CDC began distributing a data collection instrument to health departments to gather additional information on infected HCP. The instrument included questions on job type, facility type, contact with patients with novel influenza A (H1N1) infections or respiratory illness (i.e., pneumonia, upper respiratory tract infections, or influenza-like illness), and use of PPE (i.e., gloves, gowns, surgical masks, N95 respirators, or eye protection [goggles or face shield]). For this analysis, HCP were defined as employees, students, contractors, clinicians, or volunteers whose activities involved contact with patients in a health-care or laboratory setting. Only HCP with confirmed or probable novel influenza A (H1N1) infections were included in the analysis.

Reports on HCP cases were reviewed by infection-control staff members at CDC. Cases were categorized, using criteria developed for this investigation, as having potential acquisition in the community or in a health-care setting.† The criteria used to determine the most likely source of acquisition were based on exposures indicated on the data collection instrument during the 7 days preceding symptom onset. PPE use was used to assign a level of certainty (probable or possible) to patient to HCP transmission, but PPE use was not used to distinguish between acquisition in community or health-care settings.

CDC received 48 reports of confirmed or probable novel influenza A (H1N1) infection among HCP from 18 states. Detailed information on health-care exposures was obtained for 26 cases (18 confirmed and eight probable) reported from 11 states (Table 1). Dates of illness onset ranged from April 23 to May 4. Job type was available for 25 HCP: five registered nurses (20%), four nursing assistants (16%), four physicians (16%), and 12 persons in 10 other occupations.§ Two (8%) of these infected HCP were hospitalized, one of whom reported having underlying medical conditions. Neither hospitalized HCP was admitted to an intensive-care unit; no HCP died. Among the 16 HCP for whom such information was available, eight had been vaccinated for seasonal influenza since September 2008.

Among the 26 infected HCP, 12 (46%) reported caring for a patient with either novel influenza A (H1N1) infection (six) or respiratory illness (six) (Table 2). Six HCP (23%) reported having a close contact or family member with either respiratory illness (three) or novel H1N1 infection (three); four (15%) reported recent travel to Mexico. By using the criteria for assessment of infection acquisition, 13 HCP (50%) were deemed to have been infected in a health-care setting, including five instances of probable patient to HCP transmission,¶ seven of possible patient to HCP transmission, and one of probable HCP to HCP transmission. Community transmission was deemed most likely for 11 HCP (42%); two HCP (8%) had no reported exposures in either health-care or community settings.

Of the 12 HCP with probable or possible patient to HCP acquisition, 11 reported information on their use of PPE when caring for the presumed source patient. Only three reported always using either a surgical mask (two) or an N95 respirator (one) (Table 2). Five reported always using gloves. None reported always using eye protection. None reported always using gloves, gown, and either surgical mask or N95 respirator.

Among the three HCP who reported always using either a surgical mask or N95 respirator, a physician with possible patient to HCP acquisition reported always using an N95 respirator when with the presumed source patient. However, the physician also reported never having had a fit test for the respirator, and information was not available on whether the physician used a gown or eye protection (Table 3). A nurse anesthetist with possible patient to HCP transmission reported always using gloves and a surgical mask with the presumed source patient, but sometimes using a gown, N95 respirator, and eye protection. In addition, a registered nurse with possible patient to HCP transmission (who was caring for a novel H1N1 patient on droplet precautions) reported always using a surgical mask and gloves with the presumed source patient but never using a gown, N95 respirator, or eye protection.