Thursday, April 30, 2009

Influenza A (H1N1) - A Background in Pandemic

Many people around the world have heard now of the outbreak of the flu, informally nicknamed the “swine flu,” or “Mexican flu,” yet which is officially designated as a strain of Influenza A virus subtype H1N1. It is actually a unique mutation, with a combination of four strains of flu, comprised of human, avian and two separate swine flu virus elements.

As of this writing, the virus is confirmed to have spread across thirteen separate nations in North America (Canada, Costa Rica, Mexico and the U.S.), South America (Peru), Europe (Austria, Germany, Netherlands, Spain, Switzerland, U.K.), Asia (Israel), and the Pacific (New Zealand). Beyond that, there are suspected cases in 25 more nations spanning every continent barring Antarctica.

In response, the Mexican government has already decided to shutter a great deal of places of education and business, and has cancelled many events to minimize public contact. Individual schools in the United States have also closed due to localized outbreaks. Many other nations have taken extreme, seemingly irrational proactive measures, such as slaughtering pigs, or putting a ban on pork products, though there has been no evidence of a pig being infected by this strain of virus.

As of 30 April 2009, there have been at least 3,964 suspected cases around the world, with the vast majority (2,498) occurring in Mexico. Out of those suspected cases there have been 265 cases confirmed by laboratories a being the H1N1 strain. It has caused 168 suspected deaths and 9 confirmed deaths, with most of those deaths occurring in Mexico.

This puts the mortality of the virus, so far, between 3.4% - 4.2%.

Comparison With Other Influenza Outbreaks

Influenza outbreaks and related hospitalizations and deaths occur annually, and each flu season varies greatly. Even during mild years, influenza takes more lives on an annual basis than many other causes of death.

According to the World Health Organization (WHO), 5-15% of populations are generally affected. Every year worldwide, three to five million people are stricken with severe illness due to influenza, and 250,000 - 500,000 die. That equates roughly to a global mortality rate of 0.004% - 0.0075% of the total world population, and 0.02% - 0.15% for those infected with the virus.

It is sometimes not the influenza itself that kills, but the pneumonia that sets in as the body’s immune system responds. Therefore, the U.S. Center for Disease Control (CDC) commonly combines annual mortality statistics as Pneumonia/Influenza, or “P&I,” and estimates an annual death rate in the U.S. of 36,000, and hospitalizations at over 200,000. The CDC estimates between 5% - 20% of the U.S. population is affected by flu every season. Annual U.S. deaths can therefore range between 30,000 to 50,000. Which equates to an annual mortality rate between 0.01% - 0.015% of the total population, or 0.05% - 0.33% of the infected population.

Thus note that most flu outbreaks infect a large population, but are generally mostly mildly debilitating. While deaths and hospitalizations occur, they are limited to a small percentage of the affected population; with usually far less than 1% mortality rate.

In comparison, consider the avian flu outbreak of 2003-2009. It was caused by a very different strain of A(H5N1), the total number of human cases was limited to 421, but the mortality rate was very high: 257 deaths, or 61%.

The outbreak of Severe Acute Respiratory Syndrome (SARS) virus in 2002-2003 also serves as a comparative example. Out of 8,273 cases reported, there were 775 deaths. This equates to a mortality rate of 9.6%.

Right now, the current rate of mortality for the A(H1N1) virus is half that of SARS, and far less than a tenth of the lethality of the avian flu outbreak.

Influenza vs. Cholera

Another comparison to give pause is that of cholera in Zimbabwe and sub-Saharan Africa over the past year. According to the U.N. Office of the Coordination of Humanitarian Affairs, through 2 April 2009, in Zimbabwe alone there were 94,443 suspected cases of bacterial cholera and 4,127 deaths, for a fatality rate of 4.3%.

It has been confirmed to have spread to neighboring Botswana, Mozambique, South Africa, and Zambia. Other cases are reported across sub-Sarahan Africa: Angola, Burundi, Democratic Republic of Congo, Kenya, Malawi, Namibia, Nigeria, Guinea-Bissau, and Togo.

It is too early to predict the rapidity of the spread and long-term mortality rate of the present A(H1N1) virus, yet to date its mortality rate is comparable to the African cholera epidemic. However, global reaction to the cholera outbreak remains muted in comparison to the front-page news of the A(H1N1) virus.

Present and Future Considerations

Unknowns still to be determined would be why the disease has proven fatal in Mexico (and one case of a Mexican child who came to the U.S. with the infection), while other cases around the world have not proven fatal. has an article analyzing the possible impact of an influenza pandemic on the U.S. economy. Note that the actual effects of the actual present A(H1N1) influenza outbreak will vary widely from these estimates and that Health and Human Services (HHS)’s figures vary widely from those of the Department of Homeland Security (DHS).

Related TED Talks

In 2006, Dr. Larry Brilliant talked about the eradication of small pox and polio, and how influenza pandemics occur. In his talk, he mentioned the Canadian organization GPHIN, and its role in identification of SARS. From that, with his $100,000 TED prize, he created InSTEDD, a global disease tracking organization based in Palo Alto, California.

Pulitzer-prize winner Laurie Garrett spoke at TED in 2007 about the 1918 flu pandemic, and what is different between then and now. Her words are quite illuminating towards how we can, and how we may not be able to, respond as communities and governments.

Both speakers focus on the avian flu, which is a different strain than the A(H1N1) “swine” flu. Yet the overall message and information remains relevant for knowing about how to face a global influenza outbreak.

No comments:

Post a Comment