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Volume 2 No 16; 18 April 2008

 

 

Influenza B outbreaks in closed settings continue to be reported to the HPA's Centre for Infections

Influenza activity has returned to baseline levels in England. The overall influenza-like illness episode incidence rate was 8.6 per 100,000 persons in week 15/08 - below the baseline activity threshold of 30 per 100,000.

Prior to March 2008, only six outbreaks of influenza-like illness in closed settings had been reported to Centre for Infections (CfI) this winter, of which three were confirmed as due to influenza - one due to influenza A(H3) and two due to influenza B.

Since the beginning of March there have been 12 outbreaks of influenza-like illness reported from around the United Kingdom. A total of five reported in primary and secondary schools, one in a hospital ward and six in elderly care homes. Eight of the 12 outbreaks have been laboratory confirmed as due to influenza B. A total of six deaths have been associated with three of the outbreaks in residential care homes. While the number of reported outbreaks is still small and the voluntary nature of the reporting mechanism leads to bias in the data, they do indicate that influenza continues to circulate in the community.

Influenza A detections by the Respiratory Virus Unit at CfI peaked in week 02/08 while influenza B detections peaked in week 10/08 (Figure 1). This reflects the tendency of influenza B viruses to circulate later in the influenza season (October to mid-May).

All influenza B viruses analysed this season by the RVU belong to the B/Yamagata lineage (B/Florida/42006-like viruses). These viruses are distinct from the B/Victoria lineage (B/Malaysia-like virus) which is included in the 2007/08 influenza vaccine, although the vaccine will still provide some protection. Surveillance indicators suggest that the major impact of influenza B is in populations which are not targeted for vaccination. This season, the majority of influenza B isolates have been obtained from individuals less than five years of age or from young adults while less than 5% of influenza B isolates have been obtained from older adults over 65 years.

For reporting and advice on the management of influenza-like illness outbreaks in closed settings, please contact the local Health Protection Unit. Further advice on more complex situations can then be sought from the HPA Centre for Infections.

Figure 1. Total (hospital and community) influenza detection, United Kingdom, 2007-2008

 

 

Health Protection Matters, Spring 2008

The latest edition of the HPA's magazine for non-specialists, Health Protection Matters, is devoted to identification, surveillance and containment of infectious diseases. Zoonotic (Q fever, rabies), waterborne (campylobacter), healthcare-associated and respiratory (influenza, legionnellosis) infections are among the themes covered in the Spring 2008 issue.

Health Protection Matters can be viewed and downloaded from the Journals and Bulletins pages within the Publications section of the main HPA website.