Table 1. Swab samples collected in this study.

Area	Hospital/Clinic (Code)	No. of samples	“I” or “II”	Sample collection period	Remarks
Osaka	Osaka Prefectural Institute of Public Health (OS)	46	“I”	May 16, 2009–May 20, 2009
Osaka	National Hospital Organization Osaka National Hospital (OM)	16	“II”	Nov. 09, 2009–Dec 22, 2009	*1
Osaka	Osaka City General Hospital (OC)	21	“II”	Nov. 01, 2009–Dec. 01, 2009
Osaka	Higashiosaka City General Hospital (HOH)	24	“II”	Oct. 27, 2009–Nov. 06, 2009
Osaka	Toyonaka Municipal Hospital (TY)	18	“II”	Dec. 02, 2009–Jan. 04, 2010
Tokyo	National Center for Global Health and Medicine (KK)	38	“II”	Oct. 20, 2009–Jan. 06, 2010	*2,*3
Chiba	Isumi Medical Center (IS)	20	“II”	Oct. 19, 2009–Nov. 24, 2009
Chiba	Chiba Prefectural Togane Hospital (TO)	11	“II”	Oct. 14, 2009–Nov. 17, 2009
Chiba	Takahashi Clinic (TA)	4	“II”	Oct. 20, 2009–Oct. 30, 2009
Chiba	Sakuma Clinic (SA)	2	“II”	Oct. 20, 2009–Oct. 30, 2009
Chiba	Okazaki Clinic (OK)	2	“II”	Oct. 20, 2009–Oct. 27, 2009
Chiba	Matsuo Clinic (MA)	16	“II”	Oct. 13, 2009–Nov. 20, 2009
Chiba	Ito Clinic (IT)	3	“II”	Oct. 13, 2009–Nov. 20, 2009
Chiba	Furukawa Clinic (HU)	2	“II”	Oct. 22, 2009–Oct. 30, 2009
Chiba	Hokushindo Sato Clinic (HO)	18	“II”	Oct. 20, 2009–Oct. 30, 2009
Chiba	Hyuga Clinic (HI)	7	“II”	Oct. 13, 2009–Nov. 20, 2009
Chiba	Haniya Clinic (HN)	4	“II”	Oct. 20, 2009–Oct. 30, 2009
Chiba	Amano Clinic (AM)	1	“II”	Oct. 27, 2009
	Total	253

“I”, samples collected during May 16, 2009–May 20, 2009.

“II”, samples collected during October 13, 2009–January 06, 2010.

*1, N295S and A156T mutations in NA.

*2, H275Y mutation in NA (oseltamivir-resistance, severe case).

*3, D185N mutation in NA (fatal case).