Friday, August 15, 2008

Fluing Under The Radar

# 2234

Every year hundreds of millions of people come down with respiratory infections; the so-called `flu', and yet only relative handful of these patients get tested to see what kind of `flu' they have.

Often what we believe to be influenza is, in fact, some other ILI (Influenza-Like-Illness).

Here is how the CDC describes ILIs:

ILI is a nonspecific respiratory illness characterized by fever, fatigue, cough, and other symptoms. The majority of ILI cases is not caused by influenza but by other viruses (e.g., rhinoviruses and respiratory syncytial virus [RSV]), adenoviruses, and parainfluenza viruses).

Less common causes of ILI include bacteria such as Legionella spp., Chlamydia pneumoniae, Mycoplasma pneumoniae, and Streptococcus pneumoniae. Influenza, RSV, and certain bacterial infections are particularly important causes of ILI because these infections can lead to serious complications requiring hospitalization (2--4). Yearly, adults and children can average one to three and three to six ILI, respectively

As stated, on average, adults end up with 1 to 3 ILIs each year, and children average twice that number.

With a population of 300 million, we probably see on the order of 1 Billion ILIs each year in the United States alone.

Since viral infections are often mild and self-limiting, most people who contract them never seek medical care. And even if they do, doctors are generally not quick to try to identify the culprit.

Patients are likely to have recovered before the (expensive) test results could come back.

During the 2007-2008 Flu season, the CDC's surveillance program received and tested roughly 220,000 specimens for influenza.

Of these :

  • 39,453 (17.9%) were positive for Influenza
  • Of 39,453 influenza viruses, 28,105 (71.2%) were influenza A viruses
  • 11,348 (28.8%) were influenza B viruses
  • 8274 (29.4%) of the 28,105 influenza A viruses have been subtyped
  • 2,173 (26.3%) were influenza A (H1) viruses and
  • 6,101 (73.7%) were influenza A (H3) viruses.

Of the 17.9% of samples shown to have been caused by an influenza virus (A or B), less than 30% were subtyped to show the strain (H1 or H3).

It is certainly conceivable that sporadic cases of a mild, non-standard (H1 or H3) strain of influenza could circulate during flu season without being identified, even here in the United States.

As stated in the story below, the Hong Kong cases of H9N2 were only picked up by chance.

Malik Peiris, a well known microbiologist and one of the heroes of the SARS outbreak in 2003, tells us that the H9N2 virus may very well be circulating, unnoticed, in some parts of the world.

This from Reuters.

H9N2 bird flu threat understated in humans

HONG KONG (Reuters) - The H9N2 bird flu strain, identified as a possible pandemic threat, could be infecting more humans than commonly thought but its mild symptoms mean it often goes undetected, a leading Hong Kong bird flu expert said.

"It's quite possible ... H9N2 is infecting humans quite a lot, much (more) than we appreciate merely because it is beyond the radar," Malik Peiris, a Hong Kong-based microbiologist, told Reuters.

"In humans, it is very mild, so most of the time it's probably not even recognized or biologically tested," said Peiris, who has co-authored several papers on the strain in recent years.

So far, only a handful of human H9N2 cases have been documented worldwide, including four children in Hong Kong in 2003 who suffered from mild fevers and coughs -- as well as a batch in China's Guangdong province, where people often live in close proximity to poultry, Peiris said.

The Hong Kong cases were only picked up by chance given the city's rigorous influenza testing regime, Peiris said.

"It's quite a silent virus, it's not highly pathogenic ... and sometimes it causes some morbidity in poultry but by and large it is just there and it's unnoticed," Peiris said of the H9N2 strain.

(Continue. . .)

The good news is, the H9N2 virus (thus far) has only been identified as producing mild illness in humans and it is hoped that it would generate only a mild pandemic.

The bad news is, that a pandemic of H9N2 would do nothing to negate the threat posed by the H5N1 virus.

It isn't as if we get a choice of one or the other.

We could, over time, see both.