Geneva, Switzerland (GenevaLunch) – The World Health Organization (WHO) reported a 16 percent increase in 24 hours in the number of A/H1N1 (swine flu) cases worldwide, from 6,497 confirmed cases Thursday 14 May to 7,500 Friday. During the previous week, the increase was 200 percent. The statistics hide a more complex picture than the dramatic rise in numbers at first appears to show.

The number of deaths remains stable at 65, a mortality rate of about one percent, far less than the SARS outbreak in 2006. From its epicentre in Mexico and the US in late April, the disease has made inroads into every part of the world, save sub-Saharan Africa, WHO’s latest figures show. Yet overall, it remains primarily a North American disease. Ninety-five percent of all confirmed cases have been reported in Canada, the USA and Mexico.

More cases to come

The US Centers for Disease Control (CDC) predicts more cases, and more deaths, over the coming days and weeks. The agency also reports that it has developed a diagnostic tool kit (Ed. note: see GL’s article on Geneva-based virologist’s diagnostic tool), which it is sending to local health authorities. The CDC expects the rate of diagnoses to speed up as a result, with a subsequent increase in numbers. Other countries around the world are also getting better and quicker at detecting the disease, reports the BBC, so numbers reported to WHO are expected to jump. The 15 May increase could be a result of these factors, but the WHO has not issued a statement explaining the new figures.

The official US number of confirmed infections almost doubled from 8 to 9 May, not because the disease suddenly spread, but because a large batch of positive results came back from the labs. This kind of jump could well be repeated elsewhere over the next few days.

Spread of virus

Media attention has focused largely on how the virus is spread from country to country by travellers, but as the disease spreads this is shifting. The European Centre for Disease Protection and Control (ECDC), 10 May said that 36 of the then-total of 188 confirmed European cases were people who caught the disease in-country, that is from travellers returning with the disease from a risk country.

Statistical gap: people also get well and go home

Missing from the statistics are the numbers of people who eventually get sent home, either because the sniffles they had are not A/H1N1 or because they were infected but recovered. The wave of disease spreads around the world, but it is followed by a second wave of people who go home. Official statistics do not reflect this second wave. The numbers represent the cumulative caseload, not the currently infected.

In comparison, the CDC reports that 200,000 people are hospitalized yearly, on average,  for the seasonal flu and 36,000 Americans die of the flu each year.

Mapping the virus’s spread

A graphic representation of the spread of the disease is available from the WHO as well as unofficial sites such as the BBC and a site called Flu Tracker.

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