In total there were 82 titer rises among 78 participants. Of these, 13 (16%) were due to A/New Caledonia/20/ 1999 (H1N1), 64 (78%) due to either of the two A/ H3N2-strains tested, two (2%) due to B/Malaysia/2506/ 2004 and three (4%) due to B/Jiangsu/10/2003. There were four double-infections, three with H3N2/H1N1 coinfections and one with titre rises to both B strains. Table 2 shows SCII and reported infections by healthcare worker status. The overall attack rate for SCII was 10.6% (78/736). Of the 78 people with evidence of SCII, 23 (30%) reported neither ARI nor ILI, 33 (42%) reported at least one ARI but no ILI, and 22 (28%) reported at least one ILI.