Health and Medical News and Resources

General interest items edited by Janice Flahiff

[Press release] Three-quarters of people with seasonal and pandemic flu have no symptoms

 

English: Influenza positive tests reported to ...

English: Influenza positive tests reported to CDC by US WHO/NREVSS collaborating laboratories, national summary, 2008-2009: subtypes and percent positive tests (Photo credit: Wikipedia)

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 season—19% 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 transmission…A 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.”

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March 28, 2014 Posted by | Public Health | , , , , , , , , | Leave a comment

[Reblog] With CDC Seasonal Flu Data Unavailable, An Electronic Medical Record Offers a Glimpse of Early Activity Levels

Influenza

Influenza (Photo credit: hesenrre)

From the 13 October 2013 post at The Health Care Blog By IYUE SUNG

As Washington remains deadlocked on the implementation of the Affordable Care Act, the US government’s shutdown has resulted in the furlough of nearly 70% of the Centers for Disease Control‘s (CDC’s) workforce. CDC Director Tom Frieden recently shared his thoughts in a tweet. We agree whole-heartedly.  Although it’s all too easy to take the CDC staff for granted, they are the frontline sentinels (and the gold standard) for monitoring disease outbreaks.  Their ramp-down could have serious public health consequences.

We are particularly concerned about the apparent temporary discontinuation of the CDC’s flu surveillance program, which normally provides weekly reports on flu activity. Although flu season typically begins in late fall, outbreaks have occurred earlier in previous years. In 2009, flu cases started accumulating in late summer/early fall.  And given the potential for unique variants, such as the swine or avian flu, every season is unpredictable, making the need for regular CDC flu reports essential. We therefore hope to see the CDC restored to full capacity as soon as possible.

In the meantime, we would like to help by sharing data we have on communicable diseases, starting with the flu.


Because the athenahealth database is built on a single-instance, cloud-based architecture, we have the ability to report data in real time. As we have described in earlier posts, the physicians we serve are dispersed around the country with good statistical representation across practice types and sizes.

To get a read on influenza vaccination rates so far this season, we looked at more than two million patients who visited a primary care provider between August 1 and September 28, 2013 (Figure 1).  We did not include data on vaccinations provided at retail clinics, schools or workplaces.

This year’s rates are trending in parallel to rates over the last four years, and slightly below those of the 2012-2013 season. However, immunizations accelerate when the CDC, and consequently the media, announce disease outbreaks and mount public awareness campaigns.

As for the government shutdown, nearly everyone hopes for a quick end.  Should the standoff drag on, detection of the flu (or other diseases) may be delayed, in theory endangering the public. Fortunately, we currently see no evidence of an early influenza outbreak.  But recent history shows that the flu can begin spreading at any time, and once it does begin, it spreads very quickly, as shown in Figure 2.

We believe that our data provides a reliable view of seasonal flu trends. Last year, wewrote about the 2012-2013 flu season and found that patterns in our patient population (consisting of a large proportion of patients receiving immunizations in primary care settings) closely mirrored CDC trends. With that in mind, we believe that sharing our 2013-2014 data would be valuable to the health care community.

Whether our nation’s politicians can come to an agreement tomorrow or next month, we will continue to deliver reports that monitor population health and look ahead to contributing any information we can. If you have any suggestions or comments – on the flu or other diseases where up-to-date data would be valuable – please leave a comment here or e-mail me directly at isung@athenahealth.com.

Iyue Sung is the Director of Core Analytics at athenahealth. The post originally appeared on the athenahealth blog.

October 15, 2013 Posted by | Consumer Health, Health Statistics | , , , , | Leave a comment

NIH grantees rebut theory that seasonal flu strains originate in tropical regions

 

A diagram of influenza viral cell invasion and...

Viral Cell Invasion and Replication

From the 16 November 2011 Eureka News Alert article

NIH grantees rebut theory that seasonal flu strains originate in tropical regions

Influenza researchers have found that flu strains migrate back and forth between different regions of the world, evolving along the way. This is contrary to the common belief that flu strains from the tropics are the source of global seasonal epidemics.

The research appeared online on Nov. 14 in the Proceedings of the National Academy of Sciences. It was supported in part by the Centers of Excellence for Influenza Research and Surveillanceand the Influenza Genome Sequencing Project, funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.

“This study helps us to better understand why the persistence, movement and evolution of flu viruses are complex and largely unpredictable,” said NIAID Director Anthony S. Fauci, M.D. “These findings also remind us of the importance of maintaining vigilance in our global influenza surveillance efforts.”

Previous studies had shown that in general, influenza viruses in tropical regions tend to be more varied and circulate year-round rather than seasonally, like flu viruses found in temperate regions with more moderate climates. The prevailing theory had been that tropical areas of the world may be the source of flu viruses from which new seasonal flu strains originate….

none of the seven temperate and tropical regions they examined was the source of all new H3N2 flu strains in a given year. The migration pattern was more complex. Virus strains moved from one region to several others each year, and flu outbreaks were traced back to more than one source. And although the virus that migrated between Southeast Asia and Hong Kong persisted over time, its persistence was caused by the introduction of virus from the temperate regions. Therefore, the tropical regions did not maintain a source for the annual H3N2 influenza epidemics. Further, in contrast to annual flu epidemics in temperate climates, relatively low levels of genetic diversity among flu strains and no seasonal fluctuations were found in the tropical regions.

“We found that the H3N2 influenza virus population is constantly moving between regions, and every region is a potential source for new epidemics,” said Dr. Bahl. “Regions with more connections to others, such as travel centers, may contribute more to the global diversity of circulating viruses.”

The complexity of the global virus circulation found in the study suggests that efforts to control flu should include region-specific strategies, according to the researchers. In future studies, the researchers intend to examine whether the virus behaves differently in temperate and tropical areas, including regions not included in this analysis, and in places that are more or less connected to the rest of the world.

 

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The new findings build on earlier influenza virus evolution research funded in part by NIAID (http://www.niaid.nih.gov/news/newsreleases/2008/Pages/flu_evolution.aspx). For more information about NIAID’s influenza research, visit (http://www.niaid.nih.gov/topics/Flu/Pages/default.aspx).

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November 17, 2011 Posted by | Medical and Health Research News, Public Health | , , , | 1 Comment

   

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