Navigation Links
Three-quarters of people with seasonal and pandemic flu have no symptoms

Around 1 in 5 of the population were infected in both recent outbreaks of seasonal flu and the 2009 H1N1 influenza pandemic, but just 23% of these infections caused symptoms, and only 17% of people were ill enough to consult their doctor.

These findings come from a major new community-based study comparing the burden and severity of seasonal and pandemic influenza in England over 5 years, published in The Lancet Respiratory Medicine journal.

"Reported cases of influenza represent the tip of a large clinical and subclinical iceberg that is mainly invisible to national surveillance systems that only record cases seeking medical attention", explains lead author Dr Andrew Hayward from University College London, UK.

"Most people don't go to the doctor when they have flu. Even when they do consult they are often not recognised as having influenza. Surveillance based on patients who consult greatly underestimates the number of community cases, which in turn can lead to overestimates of the proportion of cases who end up in hospital or die. Information on the community burden is therefore critical to inform future control and prevention programmes."*

The Flu Watch study tracked five successive cohorts of households across England over six influenza seasons between 2006 and 2011. The researchers calculated nationally representative estimates of the incidence of influenza infection, the proportion of infections that were symptomatic, and the proportion of symptomatic infections that led to medical attention.

Participants provided blood samples before and after each season for influenza serology, and all participating households were contacted weekly to identify any cases of cough, cold, sore throat or 'flu-like illness". Any person reporting such symptoms was asked to submit a nasal swab on day 2 of illness to test for a variety of respiratory viruses using Real-Time, Polymerase Chain Reaction (RT-PCR) technology.

The results show that on average 18% of the unvaccinated community were infected with influenza each winter season19% during prepandemic seasons and 18% during the 2009 pandemic. But most (77%) of these infections showed no symptoms, and only around 17% of people with PCR-confirmed influenza visited their doctor. Compared with some seasonal flu strains, the 2009 pandemic strain caused substantially milder symptoms.

The study indicates that primary-care surveillance greatly underestimates the extent of infection and illness in the community. The rate of influenza across all winter seasons was on average 22 times higher than rates of disease recorded by the Royal College of General Practitioners Sentinel Influenza-Like Illness Surveillance Scheme.

According to Dr Hayward, "Despite its mild nature, the 2009 pandemic caused enormous international concern, expense, and disruption. We need to prepare for how to respond to both mild and severe pandemics. To do this we need more refined assessments of severity, including community studies to guide control measures early in the course of a pandemic and inform a proportionate response."

Writing in a linked Comment, Dr Peter William Horby from the Oxford University Clinical Research Unit in Vietnam says, "In view of the undoubtedly high rates of subclinical influenza infection, an important unanswered question is the extent to which mild and asymptomatic influenza infections contribute to transmissionA large number of well individuals mixing widely in the community might, even if only mildly infectious, make a substantial contribution to onward transmission."

He concludes, "Surveillance of medically attended illnesses provides a partial and biased picture, and is vulnerable to changes in consulting, testing, or reporting practices. As such, it is clear that reliable estimates of the infection and clinical attack rates during the early stages of an influenza epidemic requires the collection of standardised data across the whole range of disease severity, from the community, primary care, and secondary care."


Contact: Harry Dayantis
The Lancet

Related medicine news :

1. Normal triglyceride levels in people of African descent may hinder diagnosis of metabolic syndrome
2. Anxiety Might Help People Sniff Out Threats
3. People Carrying Guns May Appear Bigger Than They Are
4. CT Scans Deliver More Radiation to Obese People: Study
5. Good intentions bring mixed results for Haitis disabled people
6. Migraines More Likely for People With Celiac Disease, Study Says
7. People Love Talking About Themselves, Brain Scans Show
8. Older People With Dementia Cared for Mostly at Home
9. People With HIV at Higher Odds of Sudden Cardiac Death
10. People Who Lived Near World Trade Center Report More Lung Disease
11. 1 size doesnt fit all when treating blood pressure in people with diabetes, VA/U-M study suggests
Post Your Comments:
(Date:11/24/2015)... Dallas, Texas (PRWEB) , ... November 24, 2015 , ... ... of all charitable donations are made in the last five weeks of the year ... #GivingTuesday was created in 2012 to connect the nation’s charities with those individuals who ...
(Date:11/24/2015)... , ... November 24, 2015 , ... DMG Productions announced ... Begley Jr., airing first quarter 2016 via Discovery Channel. Dates and show times TBA. ... Province, and is in the business of producing and supplying medical marijuana pursuant to ...
(Date:11/24/2015)... ... November 24, 2015 , ... The Trustees, Massachusetts’ largest ... and parking fees at several of their most popular properties, including Crane Beach ... support of REI’s Black Friday #OptOutside Campaign. The Trustees encourage families and friends ...
(Date:11/24/2015)... ... 24, 2015 , ... Cancer patients, survivors, caregivers, family members ... live taping of the next CURE Connections® video series on Saturday, ... Symposium at Georgetown University Hotel & Conference Center in Washington, D.C. , CURE ...
(Date:11/24/2015)... ... ... With Thanksgiving right around the corner, holiday travel season is about to ... and vehicle. , According to the National Highway Traffic Safety Administration, 301 people were ... following safety tips from the NHTSA: , Inspect ...
Breaking Medicine News(10 mins):
(Date:11/24/2015)... , Nov. 25, 2015 WuXi PharmaTech (Cayman) ... a leading open-access R&D capability and technology platform company ... operations in China and ... at an extraordinary general meeting of shareholders held today, ... to authorize and approve the previously announced agreement and ...
(Date:11/24/2015)... , Nov. 24, 2015  Natera, ... in non-invasive genetic testing and the analysis ... it will present at the 27 th ... December 2, 2015 at 1:00 p.m. ET.  Matthew Rabinowitz, Ph.D., ... financial results, business activities and financial outlook. ...
(Date:11/24/2015)... 24, 2015  In the pharmaceutical industry, companies want ... to quickly uncover new insights, tactics and strategies that ... --> However, organizations often find it ... and ensure that all rules and regulations are met ... major barrier to efficiently launching market research projects is ...
Breaking Medicine Technology: