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Final Issue: Volume 16 Number 51

Published on: 21 December 2006

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News Archives

Last updated: Volume 14, No.23 (PDF file, 128 KB)

Archives | News Archives 2004: Page 1| News 4 June 2004

News Archives: | 2006 | 2005 | 2004 | 2003

Outbreak of influenza A (H1N1) in a school in West Sussex

 

An outbreak of influenza A (subtype H1N1) has occurred in a primary school in West Sussex.  The first cases of illness occurred during the first week of May 2004.  One child was admitted to hospital during this week with symptoms of fever, confusion, headache, and conjunctivitis.

Staff at the school reported the outbreak to the local Health Protection Unit when substantial numbers of children developed symptoms of fever, nausea, vomiting, cough, and sore throat.  Information collected through a questionnaire distributed to parents whose children had been absent from school, suggested a respiratory viral illness with a serial interval of one to three days and duration of one to seven days. 

Initial direct immunofluorescence testing of throat swabs by the local laboratory proved negative, but a serology specimen was positive for influenza A by single high titre.  The throat swabs were referred to the Health Protection Agency's Enteric, Respiratory, and Neurological Virus Laboratory (ERNVL), Colindale, where influenza A (H1N1) was detected by PCR.

The epidemic curve (figure 1) suggests that the outbreak is now over, as only low numbers of cases were reported by 26 May 2004. Overall, 125/216 (58%) of children aged between four and eight years were affected, with attack rates ranging from 44% in the reception class (aged between four and five years) to 74% in grade one (aged between five and six years). 

Figure 1 Epidemic curve for influenza A (H1N1) outbreak (averaged over weekends)


It is unusual to see an outbreak associated with influenza A (H1N1) occurring this late in the season.  Further genetic characterisation of the virus is being undertaken.   

Influenza A (H1N1) epidemiology
Influenza activity associated with subtype (H1N1) has been low over recent years.  The last substantial activity associated with this subtype occurred during the 1997/98 and 2000/01 influenza seasons when approximately 40% of the isolates characterised in each season by ERNVL were A (H1N1).  Children aged under 15 years were predominantly affected in 1997/98, and children aged under 5 years and adults aged between 15 and 44 years during 2000/01.

During 2001/02 a new subtype, influenza A (H1N2) emerged as a recombinant of previously circulating influenza A (H1N1) and (H3N2) viruses.  Since this time only sporadic isolates of influenza A (H1N1) and (H1N2) have circulated in the United Kingdom.

Outbreaks attributable to influenza have also remained low over recent years; an outbreak of influenza A (H1N1) that occurred in a primary school was reported to the Health Protection Agency's Communicable Disease Surveillance Centre (CDSC) in January 1998 (eight children), and outbreaks of A (H1N untyped) were reported in January 2002 (400/1250 children in Scotland) and March 2003 (one child who was part of a mixed outbreak of H1 and H3N2 in a school).

Influenza activity in England is currently within the range of baseline activity, having peaked early during the 2003/04 season in week 46/2003.  Between weeks 30/2003 and 20/2004 only one isolate of influenza (H1N1) and two isolates of (H1N untyped) from hospital derived specimens in children aged less under five years were detected by ERNVL, compared with 1404 detections of influenza A (H3), and five detections of influenza B. 

 

Department of Health publishes its West Nile contingency plan

The Chief Medical Officer has published a contingency plan (1) to prevent and control West Nile virus disease. Although the risk for infection in the United Kingdom (UK) remains low, there is a need to prepare for the possibility of a UK-acquired case. The contingency plan defines roles and responsibilities of parties involved in tackling the disease in the event of a UK-acquired case of WNV infection, and presents a strategy for limiting the impact of the virus.

The plan sets out measures to enhance surveillance, to alert clinicians, and to control mosquito populations. In many of these areas, action has already been taken, while in others it will be initiated only if and when a diagnosis of WNV infection is made. Surveillance of birds, mosquitoes, and horses is in progress, in addition to the human surveillance undertaken by the Health Protection Agency (HPA). Key actions for the public to protect themselves and minimise the risk of infection are included.

Given its mode of transmission, any effort to tackle WNV would require the close liaison of veterinary and health services at the local, regional, and national level. The contingency plan maps out how such co-operation would be achieved in practice through 'Public Health Action in Partnership', the formation of an inter-disciplinary incident control team to take the lead locally, and the creation of a central Government team drawn from the Department of Health, the Department for the Environment, Food and Rural Affairs, and the HPA to provide policy advice nationally.

The document broadly covers:

It is intended for all those who would have a role in protecting public health if an outbreak were to occur, including the HPA, Primary Care Trusts, Strategic Health Authorities, local authorities, and other agencies.

In preparation for this and as in previous years the HPA has launched its summer surveillance for WNV in humans from 1 June 2004. Details were published in the preceding issue of CDR Weekly volume 14, number 22, and on the HPA website, available at <http://www.hpa.org.uk/infections/topics_az/west_nile/menu.htm>.

 

References

 

1. Department of Health. West Nile virus: A contingency plan to protect the public's health. London: Department of Health, 31 May 2004. Available at
<http://www.dh.gov.uk/assetRoot/04/08/33/33/04083333.pdf>.