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Epidemiological AlertsVol. 6, No. 22

icon Update Influenza AH1N1: Regional Report (6 May 2009)



Up to 6 May 2009, the total of confirmed cases of influenza A (H1N1) recorded is 1,761 including 31 deaths, in 7 countries of the Americas (Mexico, United States, Canada, Costa Rica, Colombia, El Salvador and Guatemala).

To date, the United States has confirmed a total of 642 human cases of influenza A (H1N1) in 41 States: 4 in Alabama, 48 in Arizona, 67 in California, 17 in Colorado, 4 in Connecticut, 33 in Delaware, 5 in Florida, 3 in Georgia, 3 in Hawaii, 1 in Idaho, 122 in Illinois, 15 in Indiana, 1 in Iowa, 2 in Kansas, 2 in Kentucky, 7 in Louisiana, 1 in Maine, 4 in Maryland, 45 in Massachusetts, 8 in Michigan, 1 in Minnesota, 2 in Missouri, 4 in Nebraska, 5 in Nevada, 2 in New Hampshire, 7 in New Jersey, 3 in New México, 97 in New York, 7 in North Carolina, 5 in Ohio, 1 in Oklahoma, 15 in Oregon, 1 in Pennsylvania, 2 in Rhode Island, 16 in South Carolina, 2 in Tennessee, 61 in Texas, 1 in Utah, 3 in Virginia, 9 in Washington and 6 in Wisconsin. Other suspected cases are being investigated. 2 deaths have been registered in Texas.

From 17 April to 5 May, Mexico has reported 949 confirmed cases of influenza A (H1N1), including 31 deaths. The states with the highest number of confirmed cases are Distrito Federal, Estado de Mexico, San Luis Potosi and Hidalgo. The majority of these have occurred in previously healthy young adult people. 12% of the confirmed cases have been in children under 5 years old and 71% of the confirmed cases in persons under 30 years old.

In Canada, to date 165 human cases of influenza A (H1N1) have been confirmed (26 in Alberta, 46 in British Columbia, 2 in New Brunswick, 48 in Nova Scotia, 4 in Quebec, 1 in Manitoba, 36 in Ontario and 2 in Prince Edward Island), some of them with recent travel history to Cancun, Mexico. All the cases developed a mild form of influenza-like illness. Some of the cases presented, in addition, gastrointestinal symptoms. Indigenous transmission is not discarded since not all the confirmed cases have trip history to Mexico.

On 2 May, Costa Rica notified 1 confirmed case of influenza A (H1N1). On 3 May, Colombia reported 1 confirmed case of influenza A (H1N1), while El Salvador reported 2 confirmed cases of influenza A (H1N1). On 5 May, Guatemala notified 1 confirmed case of influenza A (H1N1) in a person that has travelled to Mexico.

Various countries of the Region are reporting suspected and probable cases. This indicates that surveillance enhancement is producing results.

International Health Regulations (IHR)

The Director-General of WHO determined on 25 April that this event constitutes a Public Health Emergency of International Concern. On 29 April, the Director General decided to raise the pandemic alert to Phase 5.

The DG recommends not closing borders or restricting travel. However, it is prudent for people who are sick to delay travel. Moreover, returning travelers who have become sick should seek medical attention in line with guidance from national authorities.


Enhanced surveillance

At this time, enhanced surveillance is recommended. On its Web page, PAHO has published orientations for the enhancement of surveillance activities, which are directed to the investigation of:

  • Clusters of cases of ILI/SARI of unknown cause
  • Severe respiratory disease occurring in one or more health workers
  • Changes in the epidemiology of mortality associated with ILI/SARI; increase of observed deaths by respiratory diseases; or increase of the emergence of severe respiratory disease in previously healthy adults/adolescents.
  • Persistent changes observed in the response to the treatment or evolution of a SARI.

The following risk factors should also cause suspicion of influenza A (H1N1):

  • Close contact with a confirmed case of influenza A (H1N1) while the case was sick.
  • Recent travel to an area where there are confirmed cases of influenza A (H1N1) have been confirmed

Virological surveillance of influenza A (H1N1)

It is recommended that National Influenza Centers (NIC) immediately submit to their regular WHO Collaborating Center for influenza all positive but unsubtypable specimens of influenza A. Shipment procedures are the same as those used by NICs for seasonal influenza specimens.

The test protocols for the detection of seasonal influenza by Polymerase Chain Reaction (PCR) cannot confirm influenza A (H1N1) cases. The Centers for Disease Control and Prevention of the United Sates (CDC) has begun to ship testing kits that will include the primers and probes as well as the required positive control samples.

Current available evidence indicates that the technique of Immunofluorescence (IF) has low sensitivity for the identification of the new influenza A virus (H1N1). As a result, its results are not recommended as a basis to rule out suspected cases. Furthermore, the suspected cases with positive results for influenza A, but unsubtypable, obtained by PCR have a high probability of being confirmed as cases of the new influenza A virus (H1N1).

Case definitions

The following case definitions are for the purpose of reporting probable and confirmed cases of influenza A (H1N1) virus infection to WHO.

Clinical case description

Acute febrile respiratory illness (fever >38°C ) with the spectrum of disease from influenza-like illness to pneumonia.

1.A Confirmed case of influenza A(H1N1) virus infection is defined as an individual with laboratory confirmed influenza A(H1N1) virus infection by one or more of the following tests*:

  • Real time RT-PCR
  • viral culture
  • four-fold rise in influenza A(H1N1) virus specific neutralizing antibodies.

2.A Probable case of influenza A(H1N1) virus infection is defined as an individual with an influenza test that is positive for influenza A, but is unsubtypable by reagents used to detect seasonal influenza virus infection OR

An individual with a clinically compatible illness or who died of an unexplained acute respiratory illness who is considered to be epidemiologically linked to a probable or confirmed case.

* Note: The test(s) should be performed according to the most currently available guidance on testing

Infection prevention and control in health care facilities

Since the main form of transmission of this disease is by droplets it is recommended strengthening the basic precautions to prevent their dissemination, for example the hygiene of hands, adequate triage in the health facilities, environmental controls, and the rational use of the personal protective equipment in accordance with the local regulations.

The complete guides “Epidemic-prone & pandemic-prone acute respiratory diseases Infection prevention & control in health-care facilities” are available at:

Last Updated on Wednesday, 06 May 2009 13:11

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