The influence of staff and resident immunization rates on influenza-like illness outbreaks in nursing homes.
OBJECTIVE
To evaluate the influence of immunization rates on the likelihood of influenza-like illness (ILI) clusters in nursing facilities.


METHODS
Retrospective cross-sectional study.


METHODS
Nursing facilities in a single for-profit chain (N = 301).


METHODS
Nursing home residents and staff in each facility.


METHODS
Resident and staff influenza immunization rates during the 2004-2005 influenza season, indicator of ILI cluster in facility defined as 3+ ILI cases reported within 72 hours in close proximity within the facility, hospitalization and mortality rates for facilities reporting ILI clusters, indicator of confirmatory laboratory testing for ILI cases in facility.


RESULTS
Staff (median = 38%) and resident (median = 85%) rates of immunization did not independently predict the likelihood of an outbreak but jointly were strong predictors. For example, facilities having greater than 55% of staff and greater than 89% of residents immunized were almost 60% less likely to have an ILI cluster (odds ratio [OR]: 0.410; 95% CI: 0.19, 0.89) compared to all others. Facilities with higher proportions of Medicaid-funded residents were less likely to have an outbreak. Each 1% increase in the proportion of residents with Medicaid was associated with a 2.5% decrease in the risk of a cluster (OR: 0.975; 95% CI: 0.956, 0.995). Bed size and staff size did not significantly influence the likelihood of an outbreak. Among facilities with outbreaks, higher vaccination rates did not predict lower rates of hospitalizations or deaths. Approximately two thirds of all ILI clusters had laboratory testing to confirm the diagnosis of influenza. Three quarters of the facilities in which outbreaks occurred and for which confirmatory tests were performed (50/67, 74.6%) had 1+ cases positively identified as influenza.


CONCLUSIONS
Both staff and residents must have high rates of vaccination to substantially alter the rate and impact of influenza outbreaks in nursing facilities.
Shugarman
Lisa R
LR
RAND Corporation, Santa Monica, CA, USA. Lisa_Shugarman@rand.org
Hales
Craig
C
Setodji
Claude Messan
CM
Bardenheier
Barbara
B
Lynn
Joanne
J
D000368:Aged; D016000:Cluster Analysis; D003428:Cross Infection / Q000453:epidemiology / Q000517:prevention & control; D003430:Cross-Sectional Studies; D004196:Disease Outbreaks / Q000517:prevention & control / Q000706:statistics & numerical data; D006282:Health Personnel / Q000706:statistics & numerical data*; D006742:Hospital Bed Capacity / Q000706:statistics & numerical data; D017052:Hospital Mortality; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007252:Influenza Vaccines; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control; D016015:Logistic Models; D008484:Medicaid / Q000706:statistics & numerical data; D015999:Multivariate Analysis; D009735:Nursing Homes / Q000458:organization & administration; D009784:Occupational Diseases / Q000453:epidemiology / Q000517:prevention & control; D016272:Occupational Health; D010561:Personnel Staffing and Scheduling / Q000706:statistics & numerical data; D011159:Population Surveillance; D012307:Risk Factors; D014481:United States / Q000453:epidemiology; D014611:Vaccination / Q000706:statistics & numerical data*
D007252:Influenza Vaccines