WHO: Many northern countries see swelling flu activity

Robert Roos

Jan 7, 2013 (CIDRAP News) – Many Northern Hemisphere countries, from North America to temperate Asia, have seen rising flu activity in recent weeks, while cases ebbed or remained scarce in most of the rest of the world, the World Health Organization (WHO) said today.

In its biweekly update, the WHO said actual virus detections have dropped in recent weeks because of the holiday season in many countries, but most countries in northern temperate regions have reported evidence of growing activity. They include countries in North America, Europe, North Africa, the eastern Mediterranean, and temperate Asia.

In Canada, for example, the consultation rate for influenza-like illness (ILI) increased from 4% in the previous update to 6.6%, with children under age 5 hardest hit. The share of respiratory samples that tested positive for flu increased from 17.8% 2 weeks ago to 31.1%. Canada reported 127 new outbreaks, up from 22 in the previous report.

Flu activity in the United States also has continued to increase, as reported here previously. Influenza A/H3N2 viruses predominated in both Canada and the United States, though influenza B was more common in the United States.

In Europe, the surge in flu activity has occurred mainly in northern and western regions, the WHO said. The agency noted that Europe's virologic pattern contrasts sharply with North America's, in that pandemic 2009 H1N1 (pH1N1) viruses made up 72% of type A isolates in the last week of December, whereas about 98% of recent US and Canadian type A isolates were H3N2.

Flu is still at low levels throughout temperate Asia, but it has increased for 5 straight weeks in northern China, prompting an official announcement of the start of the flu season there, the WHO said. All but 2% of isolates in China were type A, and 81% of the A viruses were H3N2. Both Japan and South Korea reported low activity but with some signs of increases.

Elsewhere, tropical Asia had persistent low-level flu activity, the WHO reported. Cases have declined in most countries of sub-Saharan Africa, except Ghana and the Democratic Republic of Congo, and likewise have declined to low levels in most of the Caribbean, Central America, and tropical South America.

In temperate Southern Hemisphere countries, flu remains at summer (inter-seasonal) levels, the agency said.

In a separate virologic update, the WHO said affiliated laboratories tested more than 36,000 respiratory specimens, of which 5,528 were positive for flu. Of these, 72.6% were type A and 27.4% were type B. Among the A viruses, 82.8% were H3N2 and 17.2% were pH1N1.

All Northern Hemisphere flu isolates that have been tested for antiviral resistance have remained susceptible to oseltamivir (Tamiflu) and zanamivir (Relenza), the agency reported.

The WHO also said several unconfirmed media stories about recent deaths due to pH1N1 in various places have caused some confusion. The reports sometimes refer to the virus as "swine flu," causing some readers to confuse them with other viruses recently reported in the United States, the WHO said.

The agency apparently is referring to recent swine-origin, or "variant," flu cases. In mid-December the US Centers for Disease Control and Prevention put the number of variant cases reported since July at 312, of which 308 have been H3N2 subtypes. Most of the cases were in children who were exposed to pigs at fairs. There have been no deaths among those cases.

The WHO noted that pH1N1 is now a seasonal flu virus. "As with other seasonal influenza viruses, it is expected that some deaths would occur with [pH1N1] infection, in particular now when influenza season starts in [the] Northern Hemisphere," the statement said.