US flu tide sinks in East, rises in West

Feb 1, 2013 (CIDRAP News) – Several national barometers of influenza-like illness (ILI) activity fell slightly last week as the flu weakened in the East while rising in the West, the Centers for Disease Control and Prevention (CDC) reported in its weekly update today.

In an e-mail statement, the CDC said ILI activity fell in the East but rose sharply in the West during the week of Jan 20 to 26. Twenty-four states reported high ILI activity, down from 26 a week earlier, while 13 had moderate activity, the agency update said. A CDC map shows the high levels mostly in the south-central, southwestern, and West Coast states.

Forty-two states reported geographically widespread cases last week, down from 47 states the week before. Seven states had regional activity.

ILI accounted for 4.2% of outpatient medical visits to sentinel providers last week, down a hair from 4.3% a week earlier. That compares with a national baseline level of 2.2%. By region, the levels varied from 2.4% to 6.7%.

Eight flu-related pediatric deaths were reported last week, the same number as the week before. The total for the season has reached 45, the CDC said.

The number of patients hospitalized for flu this season has reached 7,224, for a cumulative ratio of 25.9 cases per 100,000 people. The CDC said more than 50% of the patients have been age 65 or older. Of the hospital cases, 87.1% have involved influenza A.

The proportion of deaths attributed to pneumonia and flu was 9.4%, down from 9.8% the week before but still well above the epidemic threshold of 7.4%, the agency said.

The share of respiratory specimens testing positive for flu was down slightly at 25.5%, compared with 26.1% a week earlier.

On the flu vaccine front, 134.2 million doses had been distributed to providers as of Jan 25. The agency repeated its advisory that people seeking vaccination may need to call more than one provider.

Meanwhile, respiratory illness activity in Central America and the Caribbean held steady or decreased in the third week of January, the Pan American Health Organization (PAHO) reported on Jan 30. In South America, respiratory illness levels remained low or unchanged.

In Europe, flu activity continued to increase in many countries last week, but it may have passed its peak in some, particularly in northwestern Europe, the European Centre for Disease Prevention and Control (ECDC) reported today.

Two thirds of the 29 reporting countries cited medium-intensity transmission, wide geographic spread, and increasing trends, "in a range of combinations," the ECDC said.

The proportion of sentinel respiratory samples that tested positive for flu reached 52%, up from 45% a week earlier, the agency reported.

About half of the flu isolates in Europe this season have been type A and half type B, unlike the United States, where about 79% of isolates have been type A. Among type A isolates in Europe, the proportion of 2009 H1N1 viruses has increased in the last 2 weeks, from 52% of influenza A samples to 62%. That strain has been almost nonexistent in the US this winter.

See also:

CDC FluView weekly report

PAHO flu activity page

Feb 1 ECDC flu update summary

US recent flu activity summary

Flu indicator

Jan 20-26

Jan 13-19

Specimens positive

25.5%

26.1%

Outpatient ILI visits (baseline 2.2%)

4.2%

4.3%

High ILI activity states

24

26

Moderate ILI activity states

13 + DC

14

P&I deaths (threshold)

9.4% (7.4%)

9.8% (7.3%)

Pediatric deaths

8

8

Cumulative hospitalizations/100,000

25.9

22.2

Geographic extent

Widespread, states

42

47

Regional, states

7

2

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