Influence of herd immunity on norovirus: a long-term field study of repeated viral gastroenteritis outbreaks at the same facilities

Table 2 Number of facilities where repeated AG outbreaks were reported during 10 AG seasons

	K/Ns^a		PSs^a		NHs^a		Welfare facilities		Hospitals		Restaurants	Junior and senior high schools, universities	Others
Total outbreaks	504		413		256		42		31		143	16	54
Facilities	353		255		215		37		28		143	16	52
Frequency
1	259		160		186		33		25		143	16	50
2	66	(KN2-1–KN2-66)	55	(PS2-1–PS2-55)	20	(NH2-1–NH2-20)	3	(WF2-1–WF2-3)	3	(HP2-1–HP2-3)	0	0	2^b	(OT2-1, OT2-2)
3	16	(KN3-1–KN3-16)	24	(PS3-1–PS3-24)	7	(NH3-1–NH3-7)	1	(WF3-1)	0		0	0	0
4	5	(KN4-1–KN4-5)	13	(PS4-1–PS4-13)	1	(NH4-1)	0		0		0	0	0
≥ 5	7	(KNo5-1–KNo5-7)	3	(PSo5-1–PSo5-3)	1	(NHo5-1)	0		0		0	0	0

() indicates facility name listed in Additional file 3
^aK/Ns: Kindergarten/nursery schools; PSs: Primary schools; NHs: Nursing homes for the aged
^b1 child consultation center and 1 orphanage

ISSN: 1471-2334