Table 3.

Attack rate and rate ratio in the prepandemic and pandemic periods according to the setting and mode of transmission of the outbreak

Setting	Transmission mode	Period	Number of outbreaks	Number of cases	All exposed	AR (%)	RRa (95%CI)
Closed and semiclosed facilitiesb	Person to person	Pandemic	37	1,220	3,447	35.39	1.50 (1.42 to 1.57)
		Prepandemic	171	5,122	21,640	23.67	1
	Common vehicle	Pandemic	19	897	2,674	33.55	1.08 (1.02 to 1.16)
		Prepandemic	54	2,165	6,993	30.96	1
	All	Pandemic	56	2,117	6,121	34.59	1.36 (1.31 to 1.41)
		Prepandemic	225	7,287	28,633	25.45	1
Community setting	Person to person	Pandemic	6	23	46	50.00	2.68 (2.00 to 3.59)
		Prepandemic	118	1,172	6,279	18.67	1
	Common vehicle	Pandemic	43	289	1,011	28.59	0.60 (0.54 to 0.66)
		Prepandemic	294	3,181	6,690	47.55	1
	All	Pandemic	49	312	1,057	29.52	0.88 (0.80 to 0.97)
		Prepandemic	412	4,353	12,969	33.56	1
All outbreaks	Person to person	Pandemic	43	1,243	3,493	35.59	1.58 (1.50 to 1.66)
		Prepandemic	289	6,294	27,919	22.54	1
	Common vehicle	Pandemic	62	1,186	3,685	32.18	0.82 (0.78 to 0.87)
		Prepandemic	348	5,346	13,683	39.07	1
	All	Pandemic	105	2,429	7,178	33.84	1.21 (1.17 to 1.25)
		Prepandemic	637	11,640	41,602	28.00	1

Abbreviations: AR, attack rate; RR, rate ratio.

^aRate ratio taking the prepandemic period (2015–2019) as reference values.

^bNursing homes, health institutions, schools, and summer camps.