Table 1.

Rates of Severe Illness and Hospitalization during Wave 1 and Wave 2 of the 2009 Influenza A (H1N1) Pandemic, by Residence in Wisconsin, 15 April 2009 through 2 January 2010

	Residence in city of Milwaukee			Residence in Wisconsin, excluding city of Milwaukee
	Ratea		RRc (95% CI)d	Rateb		RRc (95% CI)d
Characteristic	Wave 1	Wave 2		Wave 1	Wave 2
Patients with severe illness
Hospitalized	27.9	25.3	0.9 (0.7–1.1)	1.6	16.5	10.4 (8.4–13.0)
Admitted to intensive care unit	5.3	5.8	1.1 (0.7–1.8)	0.5	3.3	6.7 (4.5–9.9)
Died	0.7	0.9	1.3 (0.3–4.7)	0.1	0.7	8.2 (3.2–20.8)
Hospitalized patients
Sex
Female	31.2	28.3	0.9 (0.7–1.2)	1.9	19.5	10.5 (7.8–14.1)
Male	24.3	22.1	0.9 (0.6–1.3)	1.7	17.3	10.4 (7.6–14.2)
Age
<18 years	39.3	26.2	0.7 (0.5–1.0)e	2.4	23.7	10.0 (6.9–14.5)
18–44 years	23.0	22.6	1.0 (0.7–1.4)	1.3	11.0	8.4 (5.6–12.5)
45–64 years	29.8	30.5	1.0 (0.7–1.6)	1.6	19.9	12.1 (8.1–18.2)
≥65 years	11.0	22.0	2.0 (0.8–5.3)	0.8	11.6	14.5 (6.3–33.2)
Race/ethnicity
White, non-Hispanic	6.0	15.0	2.5 (1.3–4.6)	1.2	11.4	9.4 (7.2–12.4)
Black, non-Hispanic	49.2	29.4	0.6 (0.4–0.8)	3.6	17.9	4.9 (2.6–9.2)
Hispanic or Latino	33.5	34.6	1.0 (0.6–1.7)	3.1	21.7	6.9 (3.4–13.9)
Asian	50.6	16.9	0.3 (0.1–1.2)	8.9	22.1	2.5 (1.2–5.2)
American Indian/Alaskan Native	0.0	0.0	…	0.0	40.7	…
Other	0.0	0.0	…	0.0	7.9	…

NOTE.  Wave 1 refers to 15 April through 30 August 2009; wave 2 refers to 31 August 2009 through 2 January 2010. Patients included were Wisconsin residents who were hospitalized ≥24 h or who died of laboratory-confirmed or probable 2009 H1N1 infection. CI, confidence interval; RR, rate ratio.

^aRate per 100,000 population, calculated using US Census Bureau's American Community Survey and Wisconsin Department of Administration City of Milwaukee 2008 population estimates.

^bRate per 100,000 population, calculated using US Census Bureau 2008 population estimates.

^cRR of wave 2 to wave 1.

^d95% CI calculated using Poisson regression.

^e95% CI is 0.45–0.99.