Investigating swine flu

Questions and issues for public health experts to consider in assessing the threat of H1N1 swine flu.

The World Health Organization declared a pandemic of H1N1 swine flu on June 11, 2009.

The announcement means the swine flu virus is spreading from person to person in a sustained manner outside of North America. Cases are mounting in Australia, the United Kingdom, Spain, Japan and Chile.

"We are satisfied that this virus is spreading to a number of countries, and it is not stoppable," WHO chief Dr. Margaret Chan said in making the formal announcement of a Phase 6 alert, which signifies a pandemic.

Declaring a pandemic signals governments to spend more on containing the virus and for drugmakers to speed up development of a swine flu vaccine, but does not necessarily mean the virus is causing more severe illnesses or deaths.

Health officials in Canada and the U.S. have already dealt with the community spread of swine flu, which WHO now acknowledges is also occurring on other continents. 

Most cases worldwide have been mild, requiring no treatment, but WHO is concerned that an increase in infections could overwhelm hospitals, particularly in poor countries.

Pandemic forecasts estimated that up to 300,000 Canadians might get sick enough with swine flu to require hospitalization.

Aboriginal people were hit hard in previous pandemics, and the UN health agency has expressed concern that some First Nations communities in northern Manitoba have experienced more severe illness from swine flu.

So far, young healthy adults and pregnant women also appear to be disproportionately affected, Chan said.

The last pandemic — the Hong Kong flu of 1968 — killed about one million people. Ordinary seasonal flu kills about 250,000 to 500,000 people each year.

"It's a little bit paradoxical. You would think that by going up a scale, that it would mean that the level of concern should go up. But really what the going up the scale would mean is that we are seeing greater spread of the virus," Dr. Keiji Fukuda, the WHO's acting assistant director general for health security and environment, said June 9.

"It does not mean that the severity of the situation has increased or that people are getting seriously sick at higher numbers or higher rates than they are right now."

The agency still considers the impact on countries to be "relatively moderate."

On April 27, the WHO raised the pandemic alert level to Phase 4, confirming that human-to-human spread of swine flu had occurred in Mexico.

Two days later, the WHO raised the alert level to Phase 5, which means the new strain of H1N1 influenza A virus that first appeared in Mexico was being regularly transmitted among people who hadn't been to Mexico.

Phase 5 indicates:

  • Sustained human-to-human transmission of a virus in at least two countries in one region.
  • Community-level outbreaks could occur.
  • The outbreak is unlikely to fizzle out.

Phase 6 includes all of the above plus a geographic spread of the virus to more than one region.

On June 5, the WHO said any future declaration of a pandemic would include information on the severity of the disease. But strictly speaking, WHO's definition of a pandemic depends only on the geographic spread of the virus, not how many people become seriously ill.

"It all comes down to how transmissible and severe it is," Dr. Michael Gardam of the Ontario Agency for Health Protection and Promotion said.

"I personally think going to Phase 6 helps on one level because it forces people to pay attention to this," he added.

People can "take planning up a notch" by thinking about making contingency plans if a lot of people fall ill, such as working from home and considering child care options if schools close.

Swine flu clearly isn't in the category of the 1918 influenza pandemic, known as the Spanish flu, in terms of death and illnesses, but the jury is still out on how many people are really sick, since not everyone gets tested.

In raising the pandemic level, the WHO considers three factors: 

1. Is the virus new?

The U.S. Centers for Disease Control said the H1N1 strain of swine flu includes genetic material from four sources: North American swine influenza viruses, North American avian influenza viruses, human influenza virus and swine influenza viruses found in Asia and Europe — a combination that has not been recognized anywhere in the world before.

2. Does it cause severe disease?

The WHO needs to weigh the differences in severity seen in some local outbreaks in Mexico, New York and First Nations reserves in northern Manitoba compared with the rest of the world.

Another infection could be at play; the genetics of the virus could differ; or there may simply not be enough cases in young adults outside of Mexico to see severe disease, experts say.

Underlying chronic diseases such as Type 2 diabetes, poverty and poor living conditions like overcrowded housing and lack of running water, as well as the legacy of previous outbreaks of respiratory diseases such as tuberculosis could also be factors, said Mary-Ellen Kelm of Simon Fraser University in Vancouver. Kelm holds the Canada Research Chair in Indigenous Peoples of North America and has studied the effect the 1918 flu pandemic had on First Nations people

"It's not acceptable," said Dr. Marsha Anderson, president of the Indigenous Physicians Association of Canada. "The housing crisis is not new in First Nation communities, [but] I think those problems are just magnified when you have an acute situation such as this."

By the end of the summer, researchers will have a better idea of how many people were infected with swine flu from antibody test results and seeing what happens in the southern hemisphere, where it is currently seasonal flu season.

Each city will bring in control measures such as closing schools and telling people to stay home when they are sick, depending on what is happening in the local area, not based on the pandemic call, Gardam noted.

In April, Fukuda said there is no good explanation for why the infection has caused so many fatalities in Mexico compared with relatively mild illnesses elsewhere.   

Researchers are looking at the ages of people who were infected, clinical studies of people who had a more severe outcome and laboratory studies of their antibodies, he added.

Seasonal flu kills about one person in 1,000, which is considered a Category 1 illness.

If the death rate for this new strain approaches 0.5 per cent to one per cent, it would be considered Category 2, said Donald Low, medical director of Ontario's public health laboratories and chief microbiologist at Toronto's Mount Sinai Hospital.

To determine the severity, researchers need information on 100 to 200 cases, including people at risk such as the elderly or those with underlying disease, Low said.

New flu viruses can also set off a harmful overreaction in the immune system called a cytokine storm that can be lethal in itself.

3. Does it move efficiently between people?

Human-to-human spread has occurred, and it's now unlikely that H1N1 will fizzle out.

The question is how easily does it move between people? Researchers are conducting studies to determine the answer. In the meantime, surveillance is critical, including for those who have not been to Mexico, said Richard Schabas, medical officer of health for Hastings and Prince Edward counties in eastern Ontario.

There are several other questions and issues for doctors and public health officials to consider.

Scientists have sequenced the virus and are growing copies of it to make diagnostic tests and potential vaccines.

So far, this H1N1 strain of swine flu responds to the oral antiviral medication oseltamivir (sold under the brand name Tamiflu) and the inhaled drug zanamivir (Relenza). Doctors in Canada and the U.S. are holding the medications in reserve because they don't want to risk the virus gaining resistance.

The value of containment measures such as masks also needs to be assessed.