Mexico, Swine Flu, and Pollution: Is There a Link?

Let me start this post by noting that, just as I am not a lawyer, I am neither a doctor or a scientist. But as those of you who read my posts (or my day blog) know, I am rarely inhibited by my ignorance.

Here's a thought about the swine flu pandemic, one I haven't seen elsewhere. To date, cases in Mexico have been far more severe than elsewhere. Many Mexicans are dying, while those affected elsewhere are, for the most part, recovering -- even though they're catching the same virus.

That got me to thinking: what could be causing the difference? I'm sure there are many, but let me suggest one that scientists may be overlooking: air pollution.

Mexico City, Mexico, ranks No. 5 on this year's list [of most polluted cities]. Residents can thank industrial and automobile emissions for air quality so bad that city ozone levels fail to meet World Health Organization standards an estimated 300 days of the year.

The WHO standards are fairly complex, and I'm not sure I could summarize them accurately. So at the risk of mixing apples and oranges, permit me to instead use the EPA's Air Quality Index (screenshot via the EPA):

Anyone who lives in a big city in the U.S. has lived through a code red day -- when people with asthma and those with weakened immune systems (such as the young and the elderly) are told to stay inside. In fact, the EPA warns that on any day when the AQI exceeds 100, "people with lung disease, older adults and children are at a greater risk from exposure to ozone, whereas persons with heart and lung disease, older adults and children are at greater risk from the presence of particles in the air."

Now look at this WaPo story from Monday:

One theory is that the virus triggers an excessively aggressive immune response that destroys the throat and lung tissue. Young adults, with the most robust immune systems, may be especially at risk. . . . Most of the fatal cases involved extensive lung damage, requiring doctors to prescribe mechanical breathing assistance. Exactly what caused the lung damage is not known.

Given the fact that Mexico City fails to meet WHO standards three hundred days a year, it's plausible to conclude that the AQI in Mexico City consistently tops 300, which the EPA describes "hazardous conditions." Were that to happen in a U.S. city, the EPA would issue "health warnings of emergency conditions [as t]he entire population is more likely to be affected."

Here's some more info on conditions in Mexico:

Mexico City is one of the world's largest metropolitan areas, housing nearly 21 million inhabitants within the Valle de Mexico. . .The Metropolitan Area of Mexico City, also called Zona Metropolitana de la Ciudad de Mexico (ZMCM), lies in a high altitude basin almost completely surrounded by hills, mountains (including dormant/active volcanoes - seismic activity is frequent and the area which is well known as an "earthquake zone." . . .

More than 20 percent of Mexico s entire population lives in the Valle de Mexico, and more than 30 percent of the country's industrial output is produced within its environs. Though already one of the world s largest cities, the Mexico City metropolitan area is still growing at a rate exceeding 3 percent annually. More than three million vehicles travel on its streets daily.

And here's what the State Department's own travel advisory had to say even before it added the warning on swine flu:

In high-altitude areas such as Mexico City (elevation 7,600 feet or about 1/2 mile higher than Denver, Colorado), most people need a short adjustment period. Reaction signs to high altitude include a lack of energy, shortness of breath, occasional dizziness, headache, and insomnia. . . . Air pollution in Mexico City and Guadalajara is severe, especially from December to May, and combined with high altitude could affect travelers with underlying respiratory problems.

In case you're wondering why pollution is particularly bad from December to May, it's probably because that's the driest time of the year. Once the rains come, they help reduce (but not eliminate) air pollution.

I used to spend a considerable amount of time in Kathmandu, Nepal. Just like Mexico City, the Kathmandu valley is located at a fairly high altitude (4,344 feet above sea level). It is surrounded by mountains, creating ideal conditions for temperature inversions, which keep pollution in and fresh air out. It has most of Nepal's factories, none of which come close to meeting U.S. environmental standards. And it has a thousands of cars, motorcycles, and motor-taxis, all of which belch tons of CO2 and nitrous oxide.

Not coincidentally, every time -- every single time -- I traveled to Kathmandu, I got a sore throat within 72 hours of arrival. It often would be accompanied by coughing, but not other symptoms usually associated with a cold or flu. Everyone in the expat community had the same experience. It was the cost of doing business.

So I don't think it's a mystery why people are dying in Mexico City and not elsewhere. Their immune systems already are compromised thanks to the pollution they're breathing in. I'll even go so far as to predict that the death rate will fall once the rains come.

Again, I'm not a scientist. But here's hoping those who are take time to explore whether there is a connection. As WHO director Margaret Chan warned today, global health crises always hit less developed countries much harder than wealthy ones. If air pollution is part of the problem, the world's poor will be the ones to suffer the most.