METHODS: From October 2004 to May 2015, respiratory specimens were received from patients with respiratory tract infection suspicion. Influenza detection was carried out by either cell culture isolation, immunofluorescence or PCR-based assays. A RT-PCR was performed to distinguish both lineages by agarose gel electrophoresis. Whole genome amplification was performed using the universal primer set by Zhou et al. in 2012, and subsequently sequenced using Roche 454 GS Junior platform. Bioinformatic analysis was performed to characterise the sequences with B/Malaysia/2506/2007 and B/Florida/4/2006 corresponding sequences as reference of (B/VIC) and (B/YAM), respectively.
RESULTS: A total of 118 FLUBV (75 FLUBV/VIC and 43 FLUBV/YAM), from 2004 to 2006, 2008-2011 and 2012-2015 seasons, were studied. The whole genome of 58 FLUBV/VIC and 42 FLUBV/YAM viruses was successfully amplified. Based on HA sequences, most FLUBV/VIC viruses (37; 64%) belonged to clade 1A (B/Brisbane/60/2008) except to 11 (19%), which fell within clade 1B (B/HongKong/514/2009) and 10 (17%) to B/Malaysia/2506/2004. Nine (20%) FLUBV/YAM viruses belonged to clade 2 (B/Massachusetts/02/2012), 18 (42%) to clade 3 (B/Phuket/3073/2013) and 15 (38%) fell within Florida/4/2006. Numerous intra-lineage reassortments in PB2, PB1, NA and NS were found in 2 2010-2011 viruses. An important inter-lineage reassortment event from 2008 to 2009 (11), 2010-2011 (26) and 2012-2013 (3) FLUBV/VIC (clade 1) strains to FLUBV/YAM (clade 3) was found, in addition to 1 reassortant NS in 2010-2011 B/VIC virus.
CONCLUSIONS: Intra- and inter-lineage reassortment episodes were revealed by WGS. While PB2-PB1-HA remained in complex, NP and NS reassortant viruses were found in both lineages. Despite reassorment events are not often, the characterisation only by HA and NA sequences might be underestimating their detection.
MATERIALS AND METHODS: During the period from 16 to 21 March 2007, outbreak investigations and active case finding were carried out among residents and nursing staff at the welfare home. Interviews and medical notes review were conducted to obtain epidemiological and clinical data. Hospitalised patients were tested for respiratory pathogens. Further genetic studies were also carried out on positive respiratory samples.
RESULTS: The overall clinical attack rate was 9.4% (17/180) in residents and 6.7% (2/30) in staff. All infected residents and staff had received influenza immunisation. Fifteen residents were hospitalised, with 2 developing severe complications. Genetic sequencing revealed that the outbreak strain had an 8.2% amino acid difference from B/Malaysia/2506/2004, the 2006 southern hemisphere influenza vaccine strain, which the residents and staff had earlier received.
CONCLUSIONS: A mismatch between the vaccine and circulating influenza virus strains can result in an outbreak in a highly immunised LTCF resident population. Active surveillance for acute respiratory illness in LTCFs could be implemented for rapid detection of antigenic drift. Enhanced infection control and other preventive measures can then be deployed in a timely manner to mitigate the effect of any outbreaks.