Flu04f

Influenza activity and influenza viruses
during the 2004-2005 epidemic season in Finland

Updated on April 27, 2005

Just two influenza A cases and one influenza B case were reported during the three summer months in 2004 to the National Infectious Disease Register in Finland. This is in contrast to the summer of 2003, when a total of 18 influenza A cases were reported, most in June but some not until in July and August. This difference encouraged to predict that during this epidemic season the outbreak may start later than in 2003/2004.

The first case of influenza A infection (a 34-year-old man from eastern Central Finland) was confirmed in week 45/2004. The virus isolate was genetically (sequencing of HA1) and antigenically (HI test) closely related to A/Wellington/1/2004 and A/Shantou/1219/2004. A similar strain was isolated in week 52 (a 24-year-old man from South-West Finland) and further three strains in week 2/2005 in South Finland. In week 3, local outbreaks of influenza A/H3 were reported among conscripts in two garrisons, one in North Finland and the other in South-East Finland. During weeks 4-6 new outbreaks occurred among conscripts in several localities in different parts of Finland, while the epidemic activity remained low in the general population. First H1N1 subtype strain (New Caledonia/20/99-like, N1 confirmed by sequencing) was isolated in week 6 in a garrison where H3 subtype strains were circulating simultaneously. First influenza B strains this epidemic season were isolated from specimens collected in week 9 from a military conscript in southern Central Finland and a civilian patient in western North Finland; antigenically (HI test) the strains were B/Jiangsu/10/2003-like. All of the H3 subtype isolates analysed antigenically so far this season (n=129) have been confirmed as A/Wellington/1/2004-like strains (not distinguished from A/California/7/2004-like strains). Influenza A/H1 and B strains have been in HI tests similar to the above reference strains. Influenza activity declined during the latter half of April in the general population; in garrisons it had declined earlier in March.

For weekly figures of laboratory-detected influenza viruses, see Table 1 and Table 2.

Table 1: Diagnostic laboratory findings of influenza made by NPHI

(data by week of sampling specimens)

INFLUENZA ISOLATES AND DETECTION OF VIRAL ANTIGENS AND RNA
YEAR	WEEK	A*	A H3	A H1	B	YEAR	WEEK	A*	A H3	A H1	B
2004	35-44	0	0	0	0	2005	1	0	0	0	0
	45	0	1	0	0		2	0	3	0	0
	46-51	0	0	0	0		3	0	15	0	0
	52	0	1	0	0		4	3	12	0	0
	53	0	0	0	0		5	0	13	0	0
	*Total*	0	2	0	0		6	0	29	1	0
							7	1	28	0	0
							8	3	13	0	0
							9	1	6	1	3
							10	2	7	0	1
							11	2	1	0	2
							12	2	3	0	0
							13	2	2	0	1
							14	2	0	0	1
							15	1	0	0	1
							*Total*	19	*132*	2	9

* Not studied for the subtype, ** Incomplete data

Table 2: Diagnostic laboratory findings of influenza made by virological laboratories in association with universities of Helsinki, Kuopio, Oulu and Turku

(data by week of report)

INFLUENZA ISOLATES AND DETECTION OF VIRAL ANTIGENS AND RNA
YEAR	WEEK	A*	A H3	A H1	B	YEAR	WEEK	A*	A H3	A H1	B
2004	35-48	0	0	0	0	2005	1	1	0	0	0
	49	1	0	0	0		2	1	0	0	0
	50-53	0	0	0	0		3	0	0	0	0
	*Total*	1	0	0	0		4	3	0	0	0
							5	0	0	0	0
							6	8	0	0	0
							7	7	0	0	0
							8	11	0	0	1
							9	18	0	0	3
							10	43	0	0	1
							11	38	0	0	3
							12	48	0	0	2
							13	21	0	0	2
							14	11	0	0	3
							15	2	0	0	2
							16	2	0	0	3
							*Total*	*214*	0	0	20