Sunday morning H1N1 musings

This morning I watched the Formula 1 race broadcast from Barcelona Spain. Although it’s difficult to discern, the stands do not appear to be anywhere near sold-out, but still, it’s a considerable crowd gathered at the track for today’s race.

Spain is a country that has an officially declared H1N1 case count of 93 as of WHO’s latest update, fourth to Mexico, United States, and Canada. North America accounts for 4,160 of the 4,379 lab confirmed cases. Considering there are only 219 confirmed cases [as of the latest WHO update] outside N. America, Spain’s 93 cases is notable.

Influenza infections during seasonal epidemics (what we face year in and year out) tend to double every three days (on average). If you have ten cases on a given day, three days later you will (on average) have 20, three days after that you will have 40, three days after that you will have 80, and so on until your community attains “herd immunity”. Herd immunity is when a community, whether our towns and cities, or the small closed communities of nursing homes, have enough recovered or vaccinated cases to no longer support forward transmission of an infectious disease.

We have our first publicly accessible estimation of what the R0 [Reproduction number] for 2009 H1N1. The R0 is important in disease outbreaks because it tells us how many new infections to expect from any other one infected person [on average].

From the New Scientist:

Warm weather may not halt swine flu

08 May 2009 by Debora MacKenzie

[Excerpts]

New data from Mexico and case numbers so far suggest that if the spread of H1N1 “swine flu” continues elsewhere as it has in the Americas, the virus could infect more than a billion people by July.

The data also suggests that the virus may not be slowed by summer temperatures in temperate countries. However, it spreads slowly enough to respond to the “social distancing” measures used in Mexico.

[snip]

“We will be moving to much more of a system like we use with seasonal flu,” which tracks levels of “flu activity”, says Besser – the number of regions in a state confirming outbreaks of flu, rather than case numbers. States such as Georgia and New York already test only serious cases.

Health experts tell New Scientist that based on the apparently exponential rate of rise soon after the WHO started counting cases, H1N1 could infect more than a billion people by July. Mexico’s numbers show just such a rise in cases of flu this spring. The Mexican health ministry thinks that would have continued without the closure of schools, businesses and mass gatherings imposed by the government.

They may be right. Based on observation of individual cases, they calculate that the R₀ of the virus in Mexico – the number of people infected by each case, a measure of how readily it spreads – is 1.4. A genetic analysis had put this at 1.16, but an underestimate was expected for technical reasons.

Mathematical modelling shows flu with low R numbers, such as 1.4, is easier to stop with “social distancing” measures.

We should view this estimate with qualified caution since many of those infected in Mexico are assumed to have self-treated.

Flu exposes flaws in Mexico’s health care system

By JOHN RICE

[Excerpted]

MEXICO CITY (AP) — Mexicans will do almost anything to avoid a public hospital emergency room, where ailing patients may languish for hours slumped on cracked linoleum floors that smell of sweat, sickness and pine-scented disinfectant.

Many don’t see doctors at all, heading instead to the clerk at the corner pharmacy for advice on coping with a cold or a flu.

So it’s no surprise that when a dangerous new swine flu virus began to sweep across Mexico, many waited too long to seek medical help — more than a week on average, according to federal Health Secretary Jose Angel Cordova.

[snip]

Mexico’s big cities have fancy private hospitals stocked with modern equipment and staffed with U.S. board-certified specialists. Americans increasingly come to Mexico for good care at low prices. The best of the public system is world-class too, with top doctors at elite centers for specialized diseases.

But Mexico’s everyday public hospital system is in crisis.

Some patients suspected of having swine flu told The Associated Press that public hospitals turned them away or forced them to wait for hours for treatment even after the government declared a national emergency.

Those who sought help before the alert — often arriving with headaches, high fevers and difficulty breathing — encountered baffled doctors who had not been warned to watch for a new virus.

[snip]

While access to health care is a right enshrined in the Mexican constitution, millions of Mexicans have no health insurance at all.

Mexico spends only 6.6 percent of its gross domestic product on health care — less than half the U.S. figure. No country in the 30-nation Organization for Economic Cooperation and Development puts a smaller share of public money into its health care system.

That means the hospitals serving most of Mexico’s 44 million poor are often crowded, ill-equipped and staffed with harried, underpaid staff working for a dizzying array of bureaucracies.

It’s so crowded, confusing and bureaucratic that the poor are more likely to head for a pharmacy, hoping to find a cheap remedy for “gripe” (pronounced GREE-pay) — a word that can cover anything from a mild cold to a deadly flu.

Most pharmacies dole out antibiotics and a host of other powerful drugs without a prescription. That encourages Mexicans to self-medicate, relying on a counter clerk’s suggestion, dosing themselves with whatever worked the last time they had a fever and waiting a day or two to see what happens.

Given the realities of Mexico’s healthcare system(s), the initial estimation of R0 is hardly definitive. That said, it is comforting that this preliminary and narrow data does not show an R0 close to or greater than 2. Once R0 approaches or passes 2 control becomes very, very difficult.

Getting back to this morning’s F-1 race in Barcelona:

As I watched, I thought about all those gathered in person, all those opportunities for a communicable disease to spread. Large gatherings are one of the things that contribute to an infectious disease’s R0, and one of the reasons influenza burns through our schools with such efficiency.

Even in our clean and modern communities, human habitation and behaviors can be very pathogen friendly.