A flu epidemic, first noted in Switzerland at the beginning of January, is continuing to grow, the federal office of public health says.

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The number of cases is increasing in all age groups across the country, save for those aged 15 to 29, the department said this week.

Overall, the number of medical consultations for the flu rose to 479 cases per 100,00 residents from 407 in the seven-period ending on Tuesday.

That's well above the minimum level of 69 consultations per 100,000 used to declare an epidemic, though its remains below the worst contagions of past years.

A map on the health department’s website shows shows the flu is widespread in all regions of the country with children aged five to 14 the most affected.

In that age group, an estimated 900 consultations with doctors for flu-like symptoms per 100,000 residents is estimated, the government figures show.

The worst-hit cantons are Ticino, Graubünden, Bern, Fribourg and Jura.

The public health office monitors the flu through its "Swiss Sentinel System", which involves reports from 200 doctors in primary healthcare.

They provide weekly reports.

Although flu-related deaths among the elderly have been reported — five cases were reported by the Geneva university hospital system (HUG) on Tuesday — the health office said “no excessive mortality has been observed”.

In fact, every year 500 to 1,000 vulnerable patients die from the flu in Switzerland every year, Darcy Christen, spokesman for CHUV, the Lausanne hospital, told the Tribune de Genève.

But these are people already at risk, including those with breathing disorders, children of a young age and elderly patients, he said.

The figures indicate that this year’s flu round is the worst since 2008-2009, but the epidemic falls well short of the levels recorded in Switzerland in 1999-2000.