Table 2. nH1N1 prevalence estimates by adjustment method and age-group, New York City, May 1 to June 19, 2009.

	Combined Data May 1–June 19	Adjustment Method 1*			Adjustment Method 2**
	Estimated ILI Percent Prevalence (95% CI)	Estimated Percent Background ILI (95% CI)	Estimated Percent nH1N1 Prevalence (95% CI)	Estimated Number with nH1N1 (95% CI)	Estimated Percent Background ILI (95% CI)	Estimated Percent nH1N1 Prevalence (95% CI)	Estimated Number with nH1N1 (95% CI)
NYC	15.8 (13.2–19.0)	8.0 (5.9–10.9)	7.8 (4.4–10.5)	639,000 (367,000–880,000)	3.6 (3.1–4.3)	12.2 (10.1–14.6)	1,017,000 (848,000–1,231,000)
Age-Group
0–17 years	26.6 (20.1–34.0)	13.5 (8.4–21.5)	13.1 (4.5–20.2)	250,000 (87,000–388,000)	6.6 (5.0–8.5)	20.0 (15.1–25.5)	383,000 (290,000–488,000)
18–64 years	13.2 (10.2–17.2)	6.6 (4.4–9.9)	6.6 (2.6–9.4)	355,000 (156,000–548,000)	2.5 (2.0–3.2)	10.8 (8.3–14.0)	582,000 (446,000–758,000)
65+ years	8.8 (6.2–12.6)	5.6 (3.0–9.8)	3.2 (0.0–6.5)	34,000 (0–68,000)	3.7 (2.6–5.4)	5.1 (3.6–7.2)	53,000 (37,000–75,000)

*Adjustment Method 1 uses survey 1 data from the less affected boroughs to estimate background ILI.

**Adjustment Method 2 uses emergency department visit data for ILI from 2004–2008 to estimate background ILI.