Influenza A (H1N1)

2009/05/08

The so-called Swine Flu has, of course, been in the news for a couple of weeks now, particularly in regards to its potential for becoming a worldwide pandemic of epic proportions. To their credit, the World Health Organization (WHO) and our own domestic Centers for Disease Control and Prevention (CDC) are generally taking it in stride; [1][2] unfortunately, the talking-head types appear to be far more prone to hyperbole (not surprising), which has led to some potential for unnecessary panic. [3] In most respects, this is really unwarranted, given that thus far, the virus appears to be fairly benign.

Looking at the statistics thus far, to date, there have been a total of 2,500 confirmed cases worldwide, [4] with a total of 46 confirmed deaths (44 in Mexico, and two in the United States). Given these two bits of information, we arrive at a mortality rate of 1.84% (46 / 2500 = 0.0184; 0.0184 x 100 = 1.84%). If the virus does reach pandemic level and infect up to 2 billion people, as the MSNBC article [*] suggests, this would lead to a death toll of 36.8 million, which is 0.613% of the total worldwide population (total population is approximately 6 billion; 36,800,000 / 6,000,000,000 = 0.00613; 0.00613 x 100 = 0.613%). Now, to be fair, 36.8 million deaths is no small number, but as a percentage of world population it is not particularly high in comparison to other pandemics throughout history.

Perhaps the most (in)famous pandemic was the Black Death, which swept across the world during the mid 1300s. [5] At that time, the overall death toll was approximately 75 million, and the world’s population of that time was roughly 450 million. [6] Taken together, this indicates that almost 17% of the world’s population died during a few decades (75,000,000 / 450,000,000 = 0.1667; 0.1667 x 100 = 16.67%). Closer to our time, the 1918 Influenza pandemic (commonly known as the Spanish Flu) is estimated to have killed from 70 to 100 million of the world’s population of roughly 1.8 billion. [7] This means that the Spanish Flu killed just under 5% of the world’s population (estimated deaths = 85 million (average of 70 and 100); 85,000,000 / 1,800,000,000 = 0.0472; 0.0472 x 100 = 4.72%). Notice also that while the both the Spanish Flu and the Black Death killed approximately the same number of people (in absolute terms), the former was not considered to be anywhere as dire as the Black Death. Of course, part of this stems from our more advanced understanding of health and illnesses, but it is also far more noticeable when 16% of the world’s population dies, as opposed to 5%. Simply put, since there were so many more people throughout the world for the Spanish Flu, the high death toll was not nearly as noticeable as it was during the Black Death.

So, what does this mean for the H1N1 outbreak thus far? First, if the current statistics remain reasonably constant (and there is evidence to suggest that it will), then we will be facing a death toll that, in absolute terms, is only half that of the Spanish Flu (and less than 1/5th as bad, in terms of its percentage effect on world population). Second, assuming that a 20% infection rate is correct for the Spanish Flu, just under 7 million people were infected each week (1,800,000,000 x 0.20 = 360,000,000; 360,000,000 / 52 = 6,923,077), and of those, 1,640,000 died (85,000,000 / 52 = 1,634,615); by comparison, the current H1N1 outbreak probably first began on 30 March 2009, which means that to date, the infection rate is roughly 500 per week (2,500 / 5 weeks since 30 March = 500), with a death rate of just over 9 per week (46 deaths  / 5 weeks = 9.2). This indicates that even though the virus may spread between individuals with relative ease, this H1N1 strain is nowhere near as virulent as the one that caused the Spanish Flu. Third, it is quite possible that the mortality results would not even be as bad as those indicated by the simple calculations above; given that the vast majority of deaths thus far have taken place in a country that is not particularly well know for its high standards of health care, [8] it is highly likely that the effects in nations with higher standards of care will be much, much lower than an abstract analysis might indicate.

One issue that could be a potential problem is that the current flu virus and the virus that caused the Spanish Flu are related strains of the same virus, though this is far from a guaranteed problem. Given that thus far, no one in the world has a proven immunity to the current strain, it is possible that the virus could mutate into a form that is far more deadly. Combined with the ease with which it appears to move from one individual to another, this potential development should be a cause for some concern. Note that I used several qualifying terms in the preceeding statements; while it is well known that micro-organisms are an excellent example of evolution in action, there are no guarantees that the resultant changes will make the virus more deadly. [9] While this certainly warrants continued observation of the disease and its spread, there really is very little reason to panic at this time. Even if the current H1N1 strain reaches pandemic level, the WHO’s own assessments indicate that it will likely cause mild symptoms, or even no symptoms at all in up to half of those who are infected. [10] So, seriously folks, as Douglas Adams was fond of writing, don’t panic.

Notes:

[1]: See here for official information from the World Health Organization’s website, last updated 08 May 2009.

[2]: See here for official information from the Centers for Disease Control & Prevention’s website, last updated 08 May 2009.

[3]: A friend posted a link [*] on his Facebook page that points to the potential for up to 2 billion total infections worldwide if the H1N1 virus becomes a true pandemic, and while his “doom and gloom” comment regarding the article is almost certainly in jest, it does hint at the potential dangers of a careless reading of the statistics mentioned.

[4]: Latest WHO update available here, from the WHO website, 08 May 2009.

[5]: History of the Black Death available here (Wikipedia article).

[6]: Historical world population statistics available here, from the U.S. Census Bureau website.

[7]: History of the Spanish Flu available here (Wikipedia article).

[8]: I do not mean to unreasonably impugn the state of Mexican health care, but from an objective stance, Mexico does not rank particularly high (or low, to their credit) compared to other nations around the world. See here for rankings from the WHO; Mexico ranks at 61 out of 190 (for comparison, the USA is at 37 of 190 – which is a little concerning to me).

[9]: Consider, for example, the case of Methicilin-resistant Stapholococcus Aureus, commonly known by the acronym, MRSA: antibiotic resistant bacteria are generally accepted to be the result of generations of bacterial survivors of antibiotic treatments, since few antibiotics produce a 100% morality rate. As a result, survivors that have previously encountered the treatment are those that have or develop a natural resistance; since these are the only bacteria that reproduce after the others were killed off by the antibiotic, the almost all of the entire subsequent generation will possess the resistence that allowed their forebears to survive. Even so, while MRSA is a significant problem within hospital settings, where it can spread easily, it has not proven to be as substantial a problem for populations outside of hospitals.

[10]: The MSNBC article [*] indicates that the WHO prediction is that 2 billion people could be infected if the virus does become a true pandemic, but alas, I was unable to locate this prediction on the WHO website. Perhaps, I was looking in the wrong places? In any event, the extant statistics support the prediction that it would be a fairly mild pandemic, if it ever achieves that level.

[*]: MSNBC article, updated 08 May 2009.

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2 Responses to “Influenza A (H1N1)”

  1. MI Says:

    IMHO, the more relevant swine flu mortality data are those for the US & Canada. These imply a mortality of far less than 1%.

    • seeker312 Says:

      Oh yeah, I know…I was projecting a worst-case scenario, also assuming that while our own domestic mortality rate would be relatively low (due to our high standards of health care), other nations around the world would not be so lucky.


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