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North America Influenza Surveillance - Week 4

 

 

 

# 5290

 


While the flu season appears to have peaked in Canada, the numbers in the United States continue to climb in the latest surveillance reports.

 

We’ve also fresh report in this week’s MMWR and CDC FluView  on another novel H3N2 swine flu virus detection in Pennsylvania dating back to last September.

 

As you will recall, last year the US saw 4 other cases, and last month China reported a case as well (see China: Single Novel Swine Flu Infection Reported).

 

First some details on this latest novel virus detection, then a brief look at the latest surveillance numbers from Canada and the United States.

 

The following comes from this week’s FluView report. I’ve bolded some of the highlights.

 

 

Novel Influenza A Virus:

One case of human infection with a novel influenza A virus was reported by the Pennsylvania Department of Health. The patient was infected with a swine origin influenza A (H3N2) virus. The patient reported contact with pigs in the week preceding symptom onset on September 6, 2010, did not require hospitalization, and has since fully recovered.

Initial testing of the specimen indicated a seasonal influenza A (H3N2) virus and the specimen was submitted to CDC as a routine surveillance sample. The delay from onset to detection occurred because attempts to culture the virus were unsuccessful. RT-PCR testing confirmed swine-origin influenza A (H3N2). Six other human infections with swine origin influenza A (H3N2) viruses have been identified in the United States during 2009 through 2010, including one other case from Pennsylvania in week 44 of 2010.

 

No epidemiologic links between this case and any of the other cases of swine-origin H3N2 infection have been identified and the viruses from all seven cases have genetic differences indicating different sources of infection.

 

There is no evidence of human-to-human transmission with this virus; however, early identification and investigation of all human infections with novel influenza A viruses is critical to evaluate the extent of the outbreak and possible human-to-human transmission. Surveillance for human infections with novel influenza A viruses continues year round.

 

For more on the potential threats posed by novel swine viruses, you wish to revisit my recent blog The (Swine) Influenza Reassortment Puzzle.

 

Moving on to Canada’s FluWatch report:

 

Summary of FluWatch Findings for the Week ending January 29, 2011

  • Overall influenza detections appear to have peaked, with most regions across the country continuing to show a decline in the percentage of positive influenza detections, with the exception of the Atlantic provinces. Other indicators of influenza activity have either decreased or remained similar to the previous week.
  • Since the beginning of the season, 88.9% of the subtyped positive influenza A specimens were influenza A/H3N2.In week 04, detections of pandemic H1N1 2009 decreased slightly as a proportion of subtyped influenza A specimens, while influenza B virus detections increased slightly. The proportion of positive tests for RSV continued to increase.

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Moving on to the United States FluView report:

 

010-2011 Influenza Season Week 4 ending January 29, 2011

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Synopsis:

During week 4 (January 23-29, 2011), influenza activity in the United States increased.

  • Of the 6,209 specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories and reported to CDC/Influenza Division, 2,044 (32.9%) were positive for influenza.
  • One human infection with a novel influenza A virus was reported.
  • The proportion of deaths attributed to pneumonia and influenza (P&I) was above the epidemic threshold.
  • Six influenza-associated pediatric deaths were reported. Four of these deaths were associated with influenza B viruses, one of these deaths was associated with an influenza A (H3) virus, and one was associated with a 2009 influenza A (H1N1) virus.
  • The proportion of outpatient visits for influenza-like illness (ILI) was 4.0%, which is above the national baseline of 2.5%. Seven of the 10 regions (Regions 1, 2, 3, 4, 5, 6, and 7) reported ILI at or above region-specific baseline levels. Seventeen states experienced high ILI activity; three states experienced
  • moderate ILI activity; New York City and 10 states experienced low ILI activity; the District of Columbia and 19 states experienced minimal ILI activity, and one state had insufficient data.
  • The geographic spread of influenza in 30 states was reported as widespread; 15 states reported regional influenza activity; the District of Columbia and one state reported local influenza activity; Puerto Rico, the U.S. Virgin Islands, and four states reported sporadic influenza activity, and Guam reported no influenza activity.

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Pneumonia and Influenza (P&I) Mortality Surveillance

During week 4, 8.5% of all deaths reported through the 122-Cities Mortality Reporting System were due to P&I. This percentage was above the epidemic threshold of 7.9% for week 4.

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Outpatient Illness Surveillance:

Nationwide during week 4, 4.0% of patient visits reported through the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) were due to influenza-like illness (ILI). This percentage is above the national baseline of 2.5%.

national levels of ILI and ARI

Related Post:

Canada
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