Table 2. Incidence rates for influenza A(H1N1)pdm09 and influenza B among persons with febrile ARI during pandemic and postpandemic periods, by age group, Ballabgarh, India*.

Age group, y	Pandemic period, November 2009–January 2010						Postpandemic period, August–October 2010					Incidence rate ratio (95% CI)
	Person-years†	Febrile ARI, no. cases	No. tested‡	No. (%) positive‡	Incidence (95% CI)§		Person-years†	Febrile ARI, no. cases	No. tested‡	No. (%) positive‡	Incidence (95% CI)§
Influenza A(H1N1)pdm09
0–5	230	499	411	71 (17.3)	375 (300–463)		498	1,174	1,036	103 (10.0)	235 (194–281)	0.6 (0.5–0.8) ¶
6–18	486	435	281	104 (37.0)	331 (282–386)		1,061	1,245	1,012	158 (15.6)	183 (158–210)	0.6 (0.4–0.7)¶
19–44	777	362	250	46 (18.4)	86 (67–110)		1,754	1,596	1,171	174 (14.9)	135 (118–153)	1.6 (1.2–2.1)#
45–59	215	135	93	9 (9.7)	61 (32–104)		493	556	413	56 (13.6)	152 (120–191)	2.5 (1.3–4.9)#
>60	128	84	59	1 (1.7)	8 (0.2–44.0)		294	362	275	15 (5.5)	68 (42–105)	8.7 (1.4–360.0)#
Influenza B
0–5	230	499	411	12 (2.9)	65 (37–108)		498	1,174	1,036	103 (10.0)	235 (194–281)	3.6 (2.1–6.6)
6–18	486	435	281	15 (5.3)	47 (30–71)		1,061	1,245	1,012	138 (13.6)	160 (137–186)	3.4 (2.2–5.5)
19–44	777	362	250	7 (2.8)	13 (6–24)		1,754	1,596	1,171	100 (8.5)	77 (65–92)	6.0 (3.2–12.8)
45–59	215	135	93	0	0 (0–17)		493	556	413	19 (4.6)	53 (34–77)	0 (0–2.9)**
>60	128	84	59	0	0 (0–29)		294	362	275	17 (6.2)	75 (47–113)	0 (0–2.4)**

*ARI, acute respiratory infection.
†For surveillance.
‡For influenza.
§Per 1,000 person-years.
¶p<0.0001 (incidence lower in postpandemic than in pandemic period).
#p<0.02 (incidence higher in postpandemic than in pandemic period).
**No influenza B–positive results for these age groups in pandemic period.