27 April 2009

Swine influenza in humans: United States, Mexico, and Canada

Human cases of swine influenza have occurred in the United States, Mexico and Canada, and have prompted the World Health Organization (WHO) to declare a public health emergency of international concern in accordance with International Health Regulations (2005) [1].

United States

On 21 April 2009 the US Centers for Disease Control and Prevention (CDC) reported two cases of a febrile respiratory illness in children in adjacent counties in southern California [2]. The children were found to be infected with a new strain of swine influenza A (H1N1) virus. Neither had contact with pigs, but one had travelled to Texas and the other to Baja California in Mexico. Both children had mild illness and recovered without specific treatment.

Surveillance for similar cases of influenza-like illness (ILI) has identified 18 other confirmed cases from southern California (5), the San Antonio area of Texas (2), Kansas (2), New York City (8) and Ohio (1) [3]. Only two of the cases were hospitalised and all have recovered.

Mexico

The Ministry of Health in Mexico have reported an increase in ILI in three areas of Mexico [4]. In the Federal District of Mexico, that includes Mexico City, an increase in ILI was detected beginning 18 March 2009, and as of 26 April there were 1,455 cases of pneumonia and 84 deaths [5]. In San Luis Potosi in central Mexico there have been 24 cases of ILI with three deaths, and in Mexicali, near the US border, there have been four cases of ILI with no deaths. Most cases have occurred in otherwise health adults. Twenty-five of the Mexican cases have been confirmed as swine influenza A (H1N1).

Canada

The Ministry of Health has confirmed six cases of human swine influenza A (H1N1); four in Nova Scotia and two from British Columbia [6].

WHO, CDC, Health Canada, the Pan American Health Organization, public health officials in Mexico and health ministries of other WHO Member States worldwide, are collaborating in investigating, providing diagnostics and implementing control measures for this rapidly evolving situation. 

Advice for travellers

At present there are no travel restrictions to any of the affected countries or regions.

Human infection with swine influenza is uncommon; approximately a single case is reported every one to two years in the United States [2]. These have usually occurred following exposure to pigs, and there has previously not been ongoing transmission from human to human. Clinical illness with swine influenza is similar to typical influenza and includes fever, cough, sore throat, body aches, headache, chills and fatigue. Some report diarrhoea and vomiting. Infection has ranged from asymptomatic and mild to severe with pneumonia and death [7, 8].

The cases in the United States and Mexico represent a new pattern; there has been an increase in cases, clustering of cases, and in certain areas, no documented exposure to pigs. These findings suggest person to person transmission.

The virus that has been isolated is a novel strain of swine influenza that has not been previously recognised, and is a combination of swine, avian and human influenza genes. The isolates have been resistant to the antivirals amantadine and rimantadine, but sensitive to oseltamivir and zanamivir. There is no information as to whether seasonal influenza vaccine will protect against swine influenza.

At present there are no travel restrictions to affected countries or areas. Travellers should be aware that influenza is transmitted via the respiratory route and exercise sensible precautions:

• follow public health guidance at your destination
• wash hands with soap and water; use waterless alcohol-based hand gels when soap and water is not available
• avoid touching your nose, mouth or eyes, to prevent the spread of germs
• cover your nose and mouth with a tissue when you cough or sneeze and dispose of the tissue promptly
• keep hard surfaces (e.g. door handles, countertops) clean using a normal cleaning solution
• assure that children follow similar advice

Travellers who have visited affected areas should monitor their health for seven days after the visit. If you develop a febrile illness with cough, sore throat, headache and muscle aches, you should:

• contact your GP or NHS Direct (0845 4647) and inform them of your travel history
• limit contact with other people
• cover your nose and mouth with a tissue when you cough or sneeze and dispose of the tissue promptly
• wash hands with soap and water
• keep hard surfaces (e.g. door handles, countertops) clean using a normal cleaning solution

Further information is available at the following sources:

HPA, Swine Influenza: http://www.hpa.org.uk/webw/HPAweb&Page&HPAwebAuto

ListName/Page/1240732817665?p=1240732817665

WHO, Swine Influenza: http://www.who.int/csr/disease/swineflu/en/index.html

CDC, Swine Influenza (flu): http://www.cdc.gov/swineflu/

References

1. World Health Organization. Swine flu illness in the United States and Mexico – update 2. 26 April 2009. Accessed 27 April 2009. Available at: http://www.who.int/csr/don/2009_04_26/en/index.html

2. Centers for Disease Control and Prevention. Swine influenza A (H1N1) infection in two children--Southern California, March-April 2009. MMWR Morb Mortal Wkly Rep 2009;58:400-2. Available at: http://www.cdc.gov/mmwr/PDF/wk/mm5815.pdf

3. Centers for Disease Control and Prevention. Human swine influenza investigation. 26 April 2009. Accessed 26 April 2009. Available at: http://www.cdc.gov/swineflu/investigation.htm

4. World Health Organization. Influenza-like illness in the United States and Mexico. 24 April 2009. Accessed 26 April 2009. Available at: http://www.who.int/csr/don/2009_04_24/en/index.html

5. Pan American Health Organization: Casos de influenza por un nuevo sub tipo: Informe Regional. 26 April 2009. Accessed 27 April 2009. Available at: http://new.paho.org/hq/index.php?lang=en

6. Public Health Agency of Canada. Government of Canada is Working Closely with Provinces and Territories and International Partners to Address Swine Flu. 26 April 2006. Accessed 27 April 2009. Available at: http://www.phac-aspc.gc.ca/media/nr-rp/2009/2009_0426_swine-eng.php

7. World Health Organization. Swine influenza frequently asked questions. 26 April 2009. Accessed 26 April 2009. Available at: http://www.who.int/csr/swine_flu/swine_flu_faq_26april.pdf

8. Myers KP, Olsen CW, Gray GC. Cases of swine influenza in humans: a review of the literature. Clin Infect Dis 2007;44:1084-8.