Risk of acquiring influenza B in a nursing home from a culture-positive roommate.

To the editor: It was recently reported that influenza A was cultured in 62 double rooms at the Wisconsin Veterans Home over six seasons. The roommate was infected in 12 (19.4%). During 3,294 resident-seasons, influenza was cultured in 208 single rooms (6.3%). Those who lived in double rooms with a culture-positive roommate had a 3.07 relative risk (95% confidence interval51.61–5.78) of acquiring influenza A. Identical methodology was used to analyze the 1992/ 1993 influenza season, in which influenza B was encountered. Case finding was based on intense prospective surveillance by research staff and has been previously described. This study compared the relative risk of influenza B in residents whose roommate had a positive culture with that of those who resided in single rooms. It is possible that a second infected roommate became infected outside of the room. To control for this possibility, the number of single rooms and the number of cases in single rooms each year were determined for comparison. Influenza B was introduced to 29 double rooms. A second culture-confirmed case was noted in 10 (34%). The second cases occurred 0 to 11 days (mean 3.9 days) after the initial case. Seven of these second cases had been vaccinated (70%). Overall, 85% of residents were vaccinated. During 489 resident-seasons in single rooms, influenza was cultured in 65 rooms (13%). Those who lived in a double room with a culture-positive roommate had a relative risk of 2.6 (95% CI51.2–5.6) of acquiring influenza B compared to those who resided in single rooms As expected, the data confirm a greater relative risk of acquiring influenza B in roommates of residents with influenza B than in residents who did not have roommates. The excess risk associated with having a culture-positive roommate is troublesome because it has been demonstrated that culture-confirmed influenza B was associated with an excess 30-day mortality of 3.9% over baseline mortality (1.5%/30 days) in nursing home residents. A private room is optimal, but this is not possible in most nursing homes. Other interventions might include using any curtain or barrier that may exist between roommates. The roommates should be counseled to maintain hand hygiene and 3-foot separation with extra environmental hygiene provided by staff. The unaffected roommate should probably be offered chemoprophylaxis with a neuraminidase inhibitor, even if the entire unit is not placed on chemoprophylaxis.