Sunday, April 26, 2009

A Primer for the Disease Management Community on Swine (H1N1) Flu

Good grief! Don your masks, don’t go out, forget about being with other people and most of all don’t even THINK about touching ANYTHING. According to dire media reports a Swine Flu Pandemic Panic of Biblical proportions is upon us.

The good news is that the Disease Management Care Blog is at your service by asking if it’s really that bad. After some research, the answer is no, but the population-care community needs to learn about this and to stay tuned. Here’s a Background, The Facts and What To Communicate primer for the DMCB readers:


Viruses are non-cellular packets of genetic material (DNA or RNA) surrounded by a membrane. Each virus species is defined by their structure, typical host (bird, pigs or human are common), lineage and subtypes. For this pandemic, it’s important to know that viruses don’t necessarily have to restrict themselves to any single species. In the case of the ‘flu’ viruses (known as the influenza viruses), they target the cells of birds, pigs and other mammals in addition to humans.

Different subtypes of influenza have varying ability to bind and enter the cells of these species, which leads to infection. The severity of the infection can vary from mild to lethal depending on both the virus as well as the host.

Influenza A is one species of virus (versus other species in influenza like ‘B’ and ‘C’) that has different subtypes. Among the influenza viruses, subtypes are based on the makeup of two surface proteins called hemagglutinin and neuraminidase.

Hemagglutinin is a type of ‘glycoprotein’ (a molecule that contains both amino acids and ‘sugar’ or oligosaccharides) that sticks out from the surface of a virus. It helps the virus stick to the surface of living cells (via the ‘sialic acid receptor). Neuraminidase is a protein that sticks out from the virus that allows newly formed virus to be released from infected cells. The structure of these two molecules contributes to their ability to attack cells, i.e., their virulence as well as their ability to change species.

Scientists have found that the individual amino acids in the hemagglutinin and neuraminidase molecules among influenza type viruses can vary. There are at least 16 main types of hemagglutinin molecules (labeled H 1 through H16) and well over a hundred different types of neuraminidases, each associated with varying virulence.

While the hemagglutinin and neuraminidase viral molecules have their own purposes, they also are targeted by the human immune system. Once recognized, these key molecules are blocked by the immune system and the virus is unable to spread.

Since viruses undergo spontaneous changes in their genetic makeup, the amino acid content of the hemagglutinin and neuraminidase can correspondingly change in small but important ways, allowing them to escape from the immune system’s recognition. There are two ways to prompt that recognition by the immune system: either an infection with the new virus (the virus causes illness until the immune system ‘kicks in’ and fights back) or immunization (an injection with weakened or even inert/dead viral protein) that prompts the system to build immunity before the real virus appears. The DMCB gets a flu shot every year because it finds it to be much easier than the alternative.

Last but not least, the clinical detection of a new influenza virus relies on a curious alliance between community-based labs and the Centers for Disease Control. It’s not routine for physicians to swab the noses of persons with flu symptoms and send it off to a local microbiology lab to try to isolate any virus. When that happens and and the local lab detects a different virus, it alerts the CDC. So, the CDC is dependent on the health care providers to take samples when they are seeing patients with the flu. When it was in practice, the DMCB rarely swabbed noses, telling persons instead to go home, drink fluids and rest. In contrast, some of the DMCB’s partners got lots of swabs.

The Facts

So with that as background, a new Influenza A virus with a hemaglugglutinin type 1 and neuraminidasetype 1 that was previously restricted to pigs appeared in lab samples from Mexico in mid March, followed by April reports in California, Texas, New York City, Kansas and then recent reports in New Zealand, Hong Kong and Spain. This particular type of Influenza A was previously isolated only from pigs or had been rarely documented to be transmitted from pigs to humans. The DMCB surmises that in the pig to human cases, the humans probably got infected because they lived in close proximity to the swine and got exposed to a large amount of virus. A new H1N1 swine influenza virus has now emerged. It has changed and can now jump from human to human, leading to hundreds being infected in Mexico. While there have been reports of many deaths in that country, that’s not true in the U.S., where infections have been described as mild with sore throat, runny nose, nausea, vomiting and diarrhea.

The DMCB thinks that all influenza infections have a mortality rate. It could be that because Mexico had many more cases, so it only appeared to have excess mortality. The next few weeks should clarify that.

In addition, while it may appear that this new virus is ‘spreading,’ it may also have been out there for more than a month. While it may be spreading, the DMCB thinks recent reports are being fueled by more docs sending off more nose swabs because they are aware of this swine flu outbreak. It’s not necessarily more cases, but more docs diagnosing more cases.

It is also possible that this virus could dissipate and simply go away. That has happened before and the fact that we’re headed into the summer season – where people don’t crowd as much and person to person transmission is decreased – may help that happen. Once again, time will tell.

What To Communicate

Influenza infection generally is a bigger threat to health among persons with chronic illness (see Box 2 here). Persons with diabetes can develop worsening of their blood glucose control, persons with chronic heart failure can experience an exacerbation of their disease and persons with lung diseases such as asthma or COPD can experience bronchospasm. Preventive advice to share with persons who are reported to be in counties with H1N1 is here and don’t forget to warn against aspirin in persons less than age 18 years.

Treatment with antiviral medications is recommended for any ill person suspected to have swine influenza A (H1N1) virus infection. The drugs to use are either zanamivir alone or with a combination of oseltamivir and either amantadine or rimantadine for five days. It’s important to note that this may change as more information on the virus becomes available.

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