Despite being relatively mild for the vast majority of those it infected, the novel H1N1 virus – at least in a small percentage of victims – showed unusual, and sometimes severe, symptoms.
The most obvious difference between the pandemic virus and seasonal influenzas of the past has been the age shift in infections, hospitalizations, and deaths.
Unlike seasonal influenza, novel H1N1 has taken its biggest toll on those under the age of 65.
While the total number of flu-related fatalities appears to be less than normally seen with seasonal flu, In terms of years of life lost, novel H1N1 was anything but benign (see Study: Years Of Life Lost Due To 2009 Pandemic).
But the difference between pandemic H1N1 and seasonal flu go beyond this profound age shift. The symptomology of this virus differed for many people as well.
A brief review, before we get to today’s study.
Researchers in Hong Kong discovered that the H1N1 virus – unlike seasonal flu – easily infects and replicates in the conjunctival tissues of the eye (see I Only Have Eyes For Flu).
Another difference observed with novel H1N1 has been its unusually high rate of gastro-intestinal symptoms. Diarrhea and vomiting have both been commonly reported with H1N1 pandemic influenza as evidenced by this report from Maggie Fox of Reuters.
Thu Oct 8, 2009 10:41pm BST
* 45 percent of those hospitalized were under 18
* Diarrhea, vomiting in 42 percent of children with H1N1
* Quick drug treatment may save lives
And in December of last year, we saw a report from the NIH on autopsies performed on H1N1 victims in New York that showed unusual levels of lung damage.
Monday, Dec. 7, 2009
In fatal cases of 2009 H1N1 influenza, the virus can damage cells throughout the respiratory airway, much like the viruses that caused the 1918 and 1957 influenza pandemics, report researchers from the National Institutes of Health (NIH) and the New York City Office of Chief Medical Examiner.
Beyond the gastro-intestinal and pulmonary symptoms, we’ve also seen a number of neurological complications, particularly (but not exclusively) in children.
The first hint of this came last summer when the CDC’s MMWR (July 23rd issue) reported on 4 pediatric patients with the novel H1N1 virus who presented with neurological symptoms including unexplained seizures and altered mental status.
. . . On May 28, 2009, the Dallas County Department of Health and Human Services (DCHHS) notified CDC of four children with neurologic complications associated with novel influenza A (H1N1) virus infection admitted to hospitals in Dallas County, Texas, during May 18--28.
In November, in a blog entitled Japan: Influenza Related Encephalopathy we looked at a report in the Yomiuri Shimbun on 132 flu patients with neurological complications during the opening four months of the pandemic.
All of which serves as prelude to today’s study by researchers at the University of Utah which is to be published later today in the Annals of Neurology (link not available yet).
Heightened Neurologic Complications in Children with Pandemic H1N1 Influenza
Jeffrey J. Ekstrand, Amy Herbener, Julia Rawlings, Beth Turney, Krow Ampofo, E. Kent Korgenski, Joshua L. Bonkowsky. Annals of Neurology; Published Online: September 20, 2010 (DOI:10.1002/ana.22184)
Since the link has not appeared, what we do have is the press release on this study:
Vaccination important to combat flu-related neurological complications
This was a retrospective study, where researchers identified 303 children hospitalized with the pandemic H1N1 virus, 18 of which developed neurological symptoms.
They compared these cases to records of 234 children admitted to the hospital in previous years due to seasonal influenza.
The most common neurological complications exhibited with novel H1N1 were seizures (12 patients or 67%), with seven exhibiting status epilepticus, a potentially life-threatening condition involving continuous or recurrent seizures that can last for a half hour or longer.
The mean age of children admitted with neurological symptoms from H1N1 was more than twice the age (6.5 years) than usually seen with seasonal flu (2.4 years).
And abnormal EEG (electroencephalogram) readings were more common in pandemic H1N1 cases than in seasonal influenza.
The researchers are unsure why these neurological manifestations appear more common in novel H1N1 influenza, but suggest that it may be part of an autoimmune response.
You can find more details of this study in an review published today by Medpage Today:
By Nancy Walsh, Staff Writer, MedPage Today
While it is easy to dismiss the 2009 pandemic virus as overblown based simply on the total number of fatalities, when one looks a little deeper one discovers that the virus played by its own set of rules.
For the demographic group usually hit hardest by the flu – those in their 70s and 80s and most likely to die from the infection - novel H1N1 was almost like a year without influenza.
But for many children, and younger adults, H1N1 proved to be a serious challenge.
This year, we’ve a double threat looming with this fall’s flu season. The (former) pandemic H1N1 virus is likely to return, along with (potentially) the new Perth H3N2 strain.
And H3N2, if it returns, is unlikely to spare the elderly as did the pandemic virus.
The good news is both of these are covered (along with an influenza B strain) in this year’s trivalent flu vaccine.
Three good reasons to get your flu shot early this year.