Table 3.

Influenza and Respiratory Syncytial Virus (RSV)‐Attributable Antibiotic Courses (Events) by Risk Group, Tennessee Medicaid Nursing Home Residents from 1995 to 1999

Risk group	Rates, Events, and Person‐Years by Season			Total Rates, Events, and Person‐Years	Estimated Annual Events Attributable to Winter Viruses per 1,000 Person‐Years* (95% Confidence Interval)		Percentage of Total Events Attributable to Winter Viruses †
	Influenza	RSV	Non‐winter viral		Influenza	RSV	Influenza	RSV	Both
No high risk					99.0 (87.2–110.9)	62.4 (43.4–81.3)	5.3	3.3	8.6
Antibiotics per 1,000 person‐years	2,263	1,844	1,716	1,881
Number of antibiotics	16,543	14,889	25,927	57,359
Person‐years	7,310	8,075	15,112	30,497
High risk					146.6 (136.4–156.8)	75.6 (58.7–92.5)	5.4	2.8	8.2
Antibiotics per 1,000 person‐years	3,331	2,674	2,503	2,734
Number of antibiotics	38,166	37,176	65,158	30,226
Person‐years	11,459	13,901	26,029	51,389

^* Values are weighted averages of annual excess events for a population of 1,000 persons within the specified age and risk group. The influenza excess events were calculated by multiplying the event rate difference between influenza and RSV by the proportion of overall study days in influenza season. The RSV excess events were calculated by multiplying the event rate difference between RSV and non‐winter‐viral season by the proportion of overall study days in RSV or influenza season (RSV circulated during both of these seasons). The weighted average difference in rates between influenza and RSV season and RSV season and non‐winter‐viral season were calculated with stratum‐specific person‐years in all seasons as weights; strata were defined by study year, race, sex, and nursing home location.

^† Percentage values are calculated by dividing the annual excess events attributable to influenza or RSV by the age and risk‐group specific total event rate.