US, Europe report declining flu markers

Apr 6, 2012 (CIDRAP News) – For the second week in a row, flu activity in the United States showed signs of decreasing, though it's too soon to say that the season has peaked, the US Centers for Disease Control and Prevention (CDC) said in an update today.

Meanwhile, flu activity in most European countries has peaked, the European Center for Disease Prevention and Control (ECDC) said yesterday in its latest update.

In the United States, the percentage of doctor's visits for flulike illness dropped slightly last week from 2.0% to 1.7%, keeping below the national baseline.

The percentage of respiratory specimens that tested positive for flu rose slightly last week, from 19.6% the previous week to 20.5%. The CDC said this indicator varied by region, ranging from 15% to 56.3%. "While influenza activity may have peaked and be declining in some states and regions, other areas may not yet have reached their peak activity level, " the CDC said in its report, warning that substantial flu activity can persist as late as May.

Deaths from pneumonia and flu dropped to 7.2%, which is below the epidemic threshold. The CDC received one more report of a pediatric flu death, bringing the season's total to 13, which is well below the number seen in a typical flu season. The child's death occurred in early March and was linked to an undetermined influenza A subtype.

H3N2 is still the dominant strain, though the profile of circulating viruses varies from region to region, as well as from state to state, the CDC said. Testing for resistance to neuraminidase inhibitors found one more 2009 H1N1 virus that was resistant, raising the total this flu season to five.

Ten states reported widespread geographic flu spread, a drop from 16 reported the previous week.

The ECDC based its assessment that the flu season has peaked in many countries on the facts that the percentage of respiratory specimens testing positive for flu at sentinel sites has fallen for 5 weeks in a row and on the decreasing trends reported by 19 countries, 15 of them for the second consecutive week.

Slovakia is the only country to report an increasing flu trend last week, the ECDC said.

The proportion of influenza B viruses detected has risen over the past 7 weeks, a pattern that the ECDC said is often seen late in the season. It said the circulating H3N2 strain is an imperfect match with the H3N2 in the seasonal flu vaccine, which is consistent with the World Health Organization's (WHO's) recommendation that the strain selection be changed for the upcoming season's vaccine. In the United States, about 20% of the H3N2 viruses that have been antigenically characterized this season have shown reduced titers with antiserum produced against the current vaccine strain.

See also:

Apr 6 CDC influenza update

Apr 5 ECDC weekly influenza update

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