In the United Kingdom the surveillance of influenza is co-ordinated and collated by the HPA Influenza Surveillance Section, Respiratory Disease Department, HPA Colindale. As influenza is not a notifiable disease and can cause a wide range of illness from a very mild or asymptomatic infection to a very serious illness which can result in hospitalisation and death, several sources of data are used to understand influenza activity in the UK. During the influenza season data from these sources are included in the weekly national influenza reports and graphs. Many of the data sources have been used for several years and some new systems were introduced in response to the pandemic in 2009.
This page describes the sources used; scroll through or click on the links below as required.
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National Pandemic Flu Service (NPFS) (used only during 2009 pandemic)
Clinical data are obtained from general practitioners (GP) surgeries that report the weekly consultations for influenza-like illness (ILI) and other acute respiratory illnesses. These schemes use the number of patients registered with the participating GP as the denominator. In the UK, each country runs their own scheme. There is also a scheme (HPA/QSurveillance system) which includes practices from across the UK* but the majority are from England. To aid interpretation of the rates and comparison with previous years, thresholds have been defined for most GP-based schemes to indicate expected rates when influenza is not circulating widely (baseline levels), when normal seasonal levels of influenza are circulating in the winter season and when higher than expected or epidemic activity is occuring (see table). These thresholds have been set based on experience with many years' of data.
Consultation rates are not directly comparable between schemes for the following reasons:
Table: GP-based surveillance schemes for influenza in the UK - click on links in first column for external websites with more information about each scheme.
|Scheme (country)||Baseline||Normal||Above average||Consultation for|
|PHA (Northern Ireland)||70||70-500||>500||ILI/influenza|
*The HPA/QSurveillance National GP System is based on data from 43% of England's population, 11% of the population in Wales, 17% in Northern Ireland and 0% in Scotland. There is also an exceptional level which is greater than 130 per 100,000; ** The thresholds for RCGP weekly returns service clinical data were lowered in 2004 (Goddard NL, Kyncl J and Watson JM. Appropriateness of thresholds currently used to describe influenza activity in England. Commun Dis Public Health 2003; 6 (3): 238-245); *** Welsh thresholds are currently being reassessed due to the use of a new surveillance system; **** The threshold level for Scotland is now based on the Pandemic Influenza Primary care Reporting (PIPeR) system which currently represents 2% of the Scottish population. HPS are currently in the process of defining thresholds for normal and above average ILI/acute respiratory infection (ARI) activity based on this system and other GP clinical surveillance systems.
Influenza-like illness (ILI) is the main indicator used for surveillance of respiratory viruses but RCGP weekly returns service and HPA/QSurveillance schemes also provide rates for other illnesses such as acute bronchitis (which can be an indicator of respiratory syncytial virus (RSV) circulation) and pneumonia. Weekly data is provided though several schemes can also provide daily data, in particular the HPA/QSurveillance scheme. This scheme involves so many GP practices (over 3500) that it is possible to compare consultation rates by Primary Care Trust (PCT).
NHS Direct is a telephone helpline service that the general public can rapidly access 24 hours a day for health related enquiries. Using specific algorithms from clinical decision support systems, nurses provide symptom-based advice to callers. The HPA/NHS Direct Syndromic Surveillance scheme has been running since 1998 and now covers the whole of England and Wales. Data on certain symptoms or syndromes are monitored with a winter focus on cold/flu and fever calls.
A similar service (NHS 24) operates in Scotland and in Northern Ireland out-of-hours centres operate. Data are available from these two schemes for surveillance purposes as well.
This was a telephone and internet service running in England between 23 July 2009 and 11 February 2010 with the aim to take pressure off primary care services due to influenza H1N1 (2009). The general public could contact this service if they had symptoms of influenza. They were taken through a series of algorithms to determine if they should receive antiviral drugs. Data were available on the number of people contacting the service, and the number who received antiviral drugs. The operation of this service affected GP consultation rates through the RCGP and HPA/QSurveillance schemes (see above) in England; it was not available in Scotland, Wales and Northern Ireland. It also affected data from the NHS Direct syndromic surveillance system as people were no longer using this service if they had influenza-like symptoms.
Internet based surveillance of influenza in the general population will be run this season through the FluSurvey project run by the London School of Hygiene and Tropical Medicine. The website is now ready to accept registrations from UK residents and the survey is planned to run from November 2011 until March 2012. The aim of this system is to provide an up to date robust system which captures influenza activity in individuals which would not otherwise be reported by health services. Participation onoly takes a few seconds each week and allows people to see in real-time the number of people in their area who are reporting illness, gives an approximate diagnosis for those who are ill and gives advice about flu and how to seek help.
Boarding schools in the MOSA scheme send reports of various illnesses, including ILI, to the Respiratory Diseases Department, CfI, each week during the school terms. Rates are calculated and relayed back to the schools. Up to 42 schools report covering a population of approximately 12,000 pupils. Most of the children are located in the southern half of England, with pupils aged between 5 and 18 years, the majority, however, are boys aged from 13 to 18 years.
Acute respiratory outbreaks in institutional setting (schools, care homes, hospitals etc.) are reported to the Respiratory Diseases Department, CfI on an ad hoc basis. Please click here to access the reporting form. CfI can provide support and advice for the management and investigation of outbreaks. Sampling to identify the virus involved is encouraged.
This flu season the Health Protection Agency is conducting a flu survey of approximately 1,000 people in England to help us understand more about the flu virus and how it affects the general population. It will be a pilot telephone survey and will be carried out by a market research company to gather data on flu from the general population. The pilot will look at the rate of clinical illness, as well as try to measure health care seeking behaviour. A cohort of participants over 18 years of age will be recruited for the study. They will be required to answer questions by telephone on whether they have been vaccinated, what their experience of the illness has been as well as how it has affected their household. They will be contacted twice during the flu season: once at the beginning (around October time) and then again after the peak of the season. In addition to this, a subset of people within the main cohort will be invited to provide a sample which the HPA can test for flu. This is a feasibility study which aims to provide an idea of how many people are actually infected with flu this forthcoming season. The preliminary findings of this survey will be published at the end of the flu season in the HPA Annual flu report. For further information about this survey, please contact the HPA at CIS@hpa.org.uk.
The Virus Reference Department (VRD) at the HPA Centre for infections, at Colindale provides a reference facility for subtyping and antigenic characterisation of influenza isolates on behalf of HPA and NHS laboratories. VRD analyses about 80% of virus isolates reported in England, Wales, and Scotland. The genetic and antigenic data derived from this analysis form the basis of data supplied from the UK to the World Health Organization as evidence to guide the annual formulation of the influenza vaccine.
In a normal influenza season, two English GP-based sentinel schemes provide timely information about the proportion of patients presenting to GPs with an influenza-like illness (ILI) who are positive for influenza and the strains of influenza that are circulating in the community:
HPA Centre for infections/Regional Microbiology Network (RMN): A sentinel network of HPA and NHS laboratories in England each recruit up to four local GPs to obtain nose and throat swabs from up to to ten patients who present with ILI each week. Specimens are examined by PCR and/or culture at collaborating laboratories for influenza, respiratory syncytial virus (RSV) and other respiratory viruses such as rhinovirus and parainfluenza. All results are forwarded to HPA Colindale and influenza-positive specimens are sent to the Virus Reference Division for subtyping and antigenic characterisation.
HPA VRD/RCGP scheme: Throughout the season about 85 general practices in the RCGP scheme (see clinical schemes above) in England obtain nose and throat swabs from patients who present with ILI and send these specimens by post to VRD for virus isolation and characterisation. Real-time PCR for influenza and respiratory syncytial virus (RSV) is carried out on specimens submitted through this scheme.
GP-based sampling schemes also operate in the Devolved Administrations (DAs) of Scotland, Wales and Northern Ireland.
Data on clinical specimens that yield positive results in tests for respiratory pathogens at regional Health Protection Agency and NHS laboratories are reported through a voluntary scheme to the Centre for Infections each week. These specimens are mainly taken for diagnostic purposes and almost all laboratories participate. The information reported includes type of specimen, method of identification, age and sex of the patient. Some reports include additional information about cases associated with outbreaks or travel. Specimens positive for influenza are also referred to the VRD at CfI for confirmation and further tests.
The initial scope of the Data Mart project was to automate the collection of all H1N1 2009 influenza laboratory testing information. Over time, the Data Mart system has evolved to incorporate all major respiratory viral test results from the majority of laboratories taking part in the extended HPA 'Swine Flu testing network'. The Data Mart system is now serving as an important laboratory surveillance tool for monitoring major respiratory viruses circulating in England. Currently the Data Mart system is using weekly automatic electronic outputs from Barts, Birmingham, Bristol, Cambridge, CFI, Kings, Leeds, Leicester, Manchester (including Preston), Newcastle, Royal Free, Southampton and UCLH laboratories. A de-duplication process is carried out when new data are uploaded into the system by using patients' surname, first name initial and date of birth. Respiratory viruses (influenza, rhinovirus, parainfluenza, adenovirus, human metapneumovirus and respiratory syncytial virus) are tested for using real time polymerase chain reaction (RT-PCR) by the participating laboratories, though not all laboratories test for or report all viruses.
As denominator data are available (the total number of patients tested for each virus) it is possible to examine trends in the proportion of samples positive for each on a weekly basis.
A sample of influenza-positive specimens are tested for susceptibility to antiviral drugs at VRD, HPA Colindale. A viral isolate can be fully tested to see if it will grow in the presence of an antiviral drug - however this can take a long time and in some cases it is not possible to grow an isolate from a sample. In the 2007/08 season a strain of H1 influenza arose which was resistant to oseltamivir (Tamiflu) and it was found that this was due to a specific genetic mutation (H275Y). Testing for this mutation is quicker than the full test, but a virus without this mutation cannot be classed as sensitive to the drug as it may have another resistance-inducing mutation. This same mutation has been detected in the influenza H1N1 (2009) virus.
From the 2010/11 season regional laboratories in England have the capability to test for antiviral resistance. All 'resistant' specimens will be confirmed at VRD.
The Health-care associated infections (HCAI) team at HPA Colindale analyse bacterial susceptibility to certain pathogens which are known to cause pneumonia as a secondary infection to influenza using data from regional laboratories. Trends in age and region over time are monitored.
A pilot scheme was set up in 2010/11 to determine the feasibility of establishing a routine surveillance system for hospitalised influenza cases. Following the success of this, severe disease surveillance is being carried out in 2011/12. There are two main systems in place:
Deaths due to influenza are difficult to estimate as they may be recorded as resulting from pneumonia or another secondary condition on the death certificate. To estimate the impact influenza has on mortality, the HPA uses data on weekly all-cause death registrations in England and Wales provided by the Office for National Statistics (ONS). Using over 20 year's of data is has been possible to establish a baseline of the expected number of deaths registered in each week. To allow for uncertainty around these figures a 90% confidence interval is calculated. If the weekly number of registered deaths is higher than the top bound of the confidence interval an excess of deaths has occurred. As these deaths are due to all causes, any excess cannot be attributed directly to influenza. EuroMoMo (Mortality Monitoring in Europe) is a project utilising an algorithm that allows age-specific and region-specific excess mortality calculation across England and Wales.
Influenza activity in other countries is monitored through the websites of the World Health Organization (WHO), the European Centre for Disease Prevention and Control (ECDC) and other individual countries public health authorities. The HPA is also responsible for reporting clinical and virological data on influenza to WHO and ECDC.
Links lead to external websites for which HPA is not responsible.
CfI: Centre for Infections, Health Protection Agency national centre involved in surveillance of infectious diseases in the UK.
Confidence interval: Gives an estimated range of values which is likely to include an unknown parameter
DA: Devolved administrations of England, Northern Ireland, Scotland and Wales
ECDC: European Centre for Disease Prevention and Control, an EU agency involved in the identification ,assessment and communication of threats to human health posed by infectious diseases.
HPA/QSurveillance system: GP-based surveillance scheme, coordinated by the HPA and the University of Nottingham.
HPS: Health Protection Scotland, health protection body in Scotland.
ILI: Influenza-like illness, a term used as other viruses can cause similar illness to influenza.
Influenza H1N1 (2009): New influenza virus first detected in North America in April 2009 (previously known as pandemic (H1N1) 2009 or 'swine flu').
MOSA: Medical Officers for Schools Association, a professional association concerned with the provision of medical care in (mainly independent) schools.
NHS: National Health Service in the UK (government funded).
NHS Direct: Nurse-led telephone help-line in England and Wales
NPFS: National Pandemic Flu Service, a service used to authorise antiviral drugs to people in England with an influenza-like illness during the pandemic of 2009 (ran from July 2009 to February 2010)
NPHS: National Public Health Service (Wales), health protection body in Wales.
ONS: Office for National Statistics (UK)
Oseltamivir (Tamiflu): Drug which prevents the spread of the influenza virus in the human body, it can be taken as treatment or prophylaxis in a person who has been exposed to the virus.
PCR: Polymerase chain reaction (PCR), a technique to amplify and detect specific pieces of DNA (e.g. from the influenza virus)
PCT: Primary Care Trust, local NHS organisations responsible for all primary health care services in England.
PHA: Public Health Agency (Northern Ireland), health protection body in Northern Ireland.
RCGP weekly returns service: Royal College of General Practitioners, a scheme involving 100 GP practices across England provides clinical surveillance data and virological specimens. This scheme has been in operation since 1968.
RMN: Regional Microbiology Network, HPA laboratories where diagnostic testing is carried out. The RMN labs take part in the GP-based sentinel virological surveillance scheme by recruiting GPs and testing samples.
RSV: Respiratory Syncytial Virus
Threshold: Levels of an indicator normally associated with certain amounts of flu activity in the community, they are based on past experience with data and are useful for interpretation and comparison with previous seasons
VRD: Virus Reference Department, HPA laboratories providing clinical advice and investigations for a wide range of human and non human primate virus infections.
Weekly National Influenza Report: A document which describes influenza activity in the UK produced by the Health Protection Agency
WHO: World Health Organization, the directing and coordinating authority for health within the United Nations system.
Last reviewed: 19 January 2012