Photo courtesy of Tim Brewer

Maybe he’s inspired by his name: Tim Brewer likes to know exactly what’s brewing. As an expert on surveillance of emerging diseases, he has worked with doctors around the globe to understand the implications of new outbreaks and to counter widespread infectious diseases including HIV/AIDS and tuberculosis. As former Program Director for the International Society for Infectious Diseases, Brewer oversaw training and service programs that reached approximately 50,000 physicians, scientists, and public health officials in over 160 countries worldwide. These programs include ProMED‐mail, one of the world’s largest publicly available outbreak reporting systems. This year, he’s been engaged in monitoring the H1N1 flu pandemic. Once you understand both what it is and how it has manifested, he says, you can see why the global health community is both concerned and a little bit relieved.

How do you track the spread of flu on an international scale?

There are a number of ways we track the spread of something like H1N1. First, government public health agencies track influenza illnesses and the culture results. So for the big picture I look at CDC, Canadian health, and the World Health Organization (WHO) data. But that data will tend to be updated once a week and they tend to be about a week behind what’s really happening, so I also look to more immediate sources, like hospitals. Hospitals track reasons people come in. In Quebec we’re seeing many patients coming in with flu-like symptoms.

And you’re seeing troubling indicators?

Well, it’s been a pandemic by definition since June 11. The technical definition of a pandemic is a virus with sustained human-to-human transmission in multiple countries within WHO regions. H1N1 reached that level very quickly. The first report of the virus was in Mexico on April 12, then the US and Canada, and the WHO called it a Level 6 pandemic in June—that’s pretty darn fast.

A lot of people have been getting this flu and recovering fairly quickly. Why is there so much uproar over it?

The uproar is primarily because this is a new virus. Until April, H1N1 was not previously circulating in humans or even in animals that we know of. So there’s no pre-existing immunity.

Influenza is an RNA virus. The RNA control replication, and they make mistakes when they replicate. Some of the changes lead to more successful viruses and some to less. Usually, the outer surface of the cell changes, causing a new seasonal flu. The H and the N of H1N1 are two proteins on the surface of the virus. That’s what our immune systems recognize when it makes antibodies. The mutations happen and the immune system has trouble recognizing the new virus. But many people still have pre-existing immunity because their immune systems have dealt with the underlying virus.

But sometimes the virus is created through what’s called an agnogenic shift. Instead of small changes on the surface of the cell, the cells swap genes with other virus cells in the host. The host could be a person, a pig (which is why it’s called swine flu), a duck—anything. And when they swap genes, instead of small changes, you get big changes. Now it’s a totally new virus. And if it’s capable of sustained human-to-human transmission, then it’s going to be a pandemic. That’s what happened in H1N1 2009. When that happens, doctors get worried about what we’re going to see.

That’s the uproar.

The other side is that this particular virus is not especially deadly. We’ve already seen the flu season in Australia and New Zealand, because they’ve had their winter. What we saw was that H1N1 outcompeted and displaced regular seasonal viruses—which might have been more deadly. Almost all the cases in those countries were H1N1. It also went through very fast. Normally flu season is 3 months; this was more like 6 weeks. In New Zealand, 7.5% of the population was infected.

And that’s likely to happen here?

This one is starting much sooner than usual in the US, and it is spreading quickly. Even though we’re seeing a lot of cases, a lot of people aren’t getting very sick, and the mortality rate isn’t very high—.004% or less. It seems to be following the pattern from New Zealand and Australia, where it spread incredibly quickly but was also over relatively quickly. But even if it’s less deadly than a regular seasonal flu, it’s still bad news. Because there’s no protective immunity, many more people than usual will get sick, so even if it’s fatal to only a tiny percentage, we’ll still see sickness—and death.