Background

In the Federal District of Mexico, surveillance began picking up cases of Influenza Like Illness(ILI) starting 18 March. The number of cases has risen steadily through April and as of 23 April there were more than 854 cases of pneumonia from the capital. Of those, 59 have died. In San Luis Potosi, in central Mexico, 24 cases of ILI, with three deaths, were reported. And from Mexicali, near the border with the United States, four cases of ILI, with no deaths, were reported at this stage.

Of the Mexican cases, 18 have been laboratory confirmed in Canada as Swine Influenza A/H1N1, while 12 of those are genetically identical to the Swine Influenza A/H1N1 viruses from California.

By 24th April, the United States Government reported seven confirmed human cases of Swine Influenza A/H1N1 in the USA (five in California and two in Texas) and nine suspect cases. All seven confirmed cases had mild Influenza-Like Illness (ILI), with only one requiring brief hospitalization.

The majority of these cases occurred in otherwise healthy young adults. Influenza normally affects the very young and the very old, but these age groups have not been heavily affected in Mexico.

Because there are human cases associated with an animal influenza virus, and because of the geographical spread of multiple community outbreaks, plus the somewhat unusual age groups affected, these events were regarded as high concern by World health Organization (WHO).

Swine influenza is a respiratory disease normally found in pigs but human cases can and does happen. The Swine Influenza A/H1N1 viruses characterized in this outbreak have not been previously detected in pigs or humans. This strain of swine influenza contains a combination of genetic material typical to avian, swine and human flu viruses. Transmission of this new swine influenza virus is thought to occur in the same way as seasonal flu. The virus that has been identified is a novel influenza A virus. The virus is sensitive to oseltamivir and zanamivir, but resistant to amantadine and rimantadine. Most reported cases of this infection outside of Mexico have recovered fully, without the need for medical attention or antiviral.

Cases have presented with symptoms of influenza-like illness: fever (≥38◦C) or history of fever and either flu-like illness (two or more of the following symptoms: cough, sore throat, rhinorrhea, limb/joint pain, headache) or other severe/life-threatening illness suggestive of an infectious process. Some cases in America have also presented with vomiting and diarrhoea. Cases of severe respiratory disease, including deaths, have been reported. Human-to-human transmission of swine has now occurred.

Based on epidemiological data, human-to-human transmission has been demonstrated along with the ability of the virus to cause community-level outbreaks which together suggest the possibility of sustained human-to-human transmission. Health-care facilities now face the challenge of providing care for patients infected with A (H1N1) swine influenza. It is critical that health-care workers use appropriate infection control precautions when caring for patients with influenza-like symptoms, particularly in areas affected by outbreaks of A (H1N1) swine influenza, in order to minimize the possibility of transmission among themselves, to other health-care workers, patients and visitors. Human-to-human transmission of A (H1N1) swine influenza virus appears to be mainly through droplets. Therefore, the infection control precautions for patients with suspected or confirmed A (H1N1) swine influenza and those with influenza-like symptoms should prioritize the control of the spread of respiratory droplets. The precautions for influenza virus with sustained human-to-human transmission (e.g. pandemic-prone influenza) are described in detail in the document “Infection prevention and control of epidemic- and pandemic-prone acute respiratory diseases in health care WHO Interim Guidelines”. This guidance may change as new information becomes available.

Fundamentals of infection prevention strategies

1. Administrative controls are key components, including: implementation of Standard and Droplet Precautions; avoid crowding, promote distance between patients (≥ 1 m); patient triage for early detection, patient placement and reporting; organization of services; policies on rational use of available supplies; policies on patient procedures; strengthening of infection control infrastructure.

2. Environmental/engineering controls, such as basic health-care facility infrastructure.

3. Adequate ventilation, proper patient placement, and adequate environmental cleaning can help reduce the spread of some respiratory pathogens during health care.

4. Rational use of available personal protective equipment (PPE) and appropriate hand hygiene.