Friday, February 24, 2017

WHO H7N9 Risk Assessment - Feb 2017


Yesterday the World Health Organization released a new Influenza at the human-animal interface report - one that reflects information provided by the Chinese government through February 14th of this year.  As new cases continue to be announced - and others are presumably in the `pipeline' - case totals increase almost daily.
As the chart above illustrates, H7N9 cases this winter have already exceeded anything we've seen to date, and China's winter epidemic season typically has a couple of more months to run.
The cases reported reflect the `sickest of the sick' - those ill enough to require hospitalization - and so we really don't have a good handle on how many mild or moderate cases there may be.  The assumption is that number is substantial (see Beneath The H7N9 Pyramid).

Despite this abrupt increase in cases, we've seen no evidence of sustained or efficient human-to-human transmission of the virus.  Clusters have been small, and infrequently reported.  For cases where information is known, the vast majority appear to have had recent close contact with live poultry. 
Today's report does not address the recent HPAI variant viruses detected in both Taiwan and Guangdong Province (see Two H7N9 `Variants' Isolated From Human Cases) in January, as this report was compiled prior to those announcements.  So far, we've not seen any indication that these genetic changes increase the health risk to humans.

Today's report also details two swine origin H1N1 infections in Europe, and contains a line listing of H7N9 cases.   Follow the link to read the full report.

Influenza at the human-animal interface
Summary and assessment, 17 January to 14 February 2017

  • New infections1: Since the previous update, new human infections with influenza A(H7N9) andA(H1N1)v viruses were reported.
  • Risk assessment: The overall public health risk from currently known influenza viruses at thehuman-animal interface has not changed, and the likelihood of sustained human-to-humantransmission of these viruses remains low. Further human infections with viruses of animalorigin are expected.
  • IHR compliance: All human infections caused by a new influenza subtype are required to be reported under the International Health Regulations (IHR, 2005).2 This includes any animal andnon-circulating seasonal influenza viruses. Information from these notifications is critical toinform risk assessments for influenza at the human-animal interface.

Avian Influenza Viruses

Avian influenza A(H5) viruses

Current situation:

Since the last update, no new laboratory-confirmed human cases of influenza A(H5) virus infection were reported to WHO. Influenza A(H5) subtype viruses have the potential to cause disease in humans and thus far, no human cases, other than those with influenza A(H5N1) and A(H5N6) viruses, have been reported to WHO. According to reports received by the World Organisation for Animal Health (OIE), various influenza A(H5) subtypes continue to be detected in birds in West Africa, Europe and Asia. There have also been numerous detections of influenza A(H5N8) viruses in wild birds and domestic poultry in several countries in Africa, Asia and Europe since June 2016. For more information on the background and public health risk of these viruses, please see the WHO assessment of risk associated with influenza A(H5N8) virus here.

Avian influenza A(H7N9) viruses

Current situation:

During this reporting period, 305 laboratory-confirmed human cases of influenza A(H7N9) virus infection were reported to WHO from China. Case details are presented in the table in the Annex of this document. For additional details on these cases and public health interventions, see the Disease Outbreak News, and for analysis of recent scientific information on the A(H7N9) influenza virus, please see a recent WHO publication here.

1 For epidemiological and virological features of human infections with animal influenza viruses not reported in this assessment, see the yearly report on human cases of influenza at the human-animal interface published in the Weekly Epidemiological Record.
2 World Health Organization. Case definitions for the four diseases requiring notification in all
circumstances under the International Health Regulations (2005).

As of 14 February 2017, a total of 1223 laboratory-confirmed cases of human infection with avian influenza A(H7N9) viruses, including at least 380 deaths3, have been reported to WHO (Figure 2). According to reports received by the Food and Agriculture Organization (FAO) on surveillance activities for avian influenza A(H7N9) viruses in China4, positives among virological samples continue to be detected mainly from live bird markets, vendors and some commercial or breeding farms.

Risk Assessment:

1. What is the likelihood that additional human cases of infection with avian influenza A(H7N9) viruses will occur? Most human cases are exposed to the A(H7N9) virus through contact with infected poultry or contaminated environments, including live poultry markets. Since the virus continues to be detected in animals and environments, further human cases can be expected. Additional sporadic human cases of influenza A(H7N9) in other provinces in China that have not
yet reported human cases are also expected.

2. What is the likelihood of human-to-human transmission of avian influenza A(H7N9) viruses? Even though small clusters of cases have been reported, including those involving healthcare workers, current epidemiological and virological evidence suggests that this virus has not acquired the ability of sustained transmission among humans, thus the likelihood is low.

3 Total number of fatal cases is published on a monthly basis by China National Health and Family Planning Commission.
4 Food and Agriculture Organization. H7N9 situation update.

3. What is the risk of international spread of avian influenza A(H7N9) virus by travellers? Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this were to occur, further community level spread is considered unlikely as this virus has not acquired the ability to transmit easily among humans.
          (Continue . . . .)

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