The unfolding of a pandemic (1) - How ‘pig flu’ learned to fly…

THE World Health Organisation began to post global updates on human infection with the Mexican swine influenza virus A/H1N1 on 26 April 2009, but the index alert on this new human-to-human influenza infection occurred several weeks earlier in the Mexican highland state of Veracruz. In early April, local health officials declared a health alert based on a respiratory disease outbreak in La Gloria, Perote Municipality, Veracruz State, Mexico. 

The La Gloria residents described a “strange” outbreak of acute respiratory infection, which led to bronchial pneumonia in some young children; symptoms included fever, severe cough, and large amounts of phlegm.  Health officials reported 400 cases that sought medical treatment in a week in La Gloria, which has a population of 3,000; approximately 1,800 cases (or 60% of the town’s population) were affected in a short time interval. La Gloria residents believed the sudden outbreak had originated from pig breeding farms located in the area.

On 16 April the Heath officials in the Mexican state of Oaxaca reported that rumours were circulating that human coronavirus was spreading within a large hospital in their state. They defined it as an atypical pneumonia however neither avian influenza nor coronaviruses, including that which causes severe acute respiratory syndrome (SARS), were identified as the source of these infections.

On 20 April the United States Centre for Disease Control in Atlanta Georgia notified other disease tracking organizations that they were already dealing with the human cases of a recently detected H1N1 ‘swine influenza’ in California and possibly Texas.

On 21 April Veratect - an independent & international biosurveillance organization [1] - alerted the International Federation of Red Cross about the increase in hospital admissions for respiratory illnesses in several states of Mexico and the coincidental detection of human cases of a new influenza virus in California and Texas. Veratect moved to notify several US state and local public health authorities, providing the caveat that the situation in Mexico remained unclear due to pending laboratory results.  Veratect contacted the Pan-American Disaster Response Unit (PADRU) and World Health Organization (WHO), informing them the Veratect team was monitoring these developments. 

On 22 April, Veratect reported the Oaxaca Health Department had 16 employees at the Hospital Civil Aurelio Valdivieso in Oaxaca, Mexico had contracted a respiratory disease. Also on that day the Mexican Ministry of Health confirmed an “unusual” outbreak of confirmed influenza had caused five human deaths between 17 and 19 April in Mexico City with approximately 120 influenza cases hospitalized throughout the capital.

The Mexican Health Secretary announced there was an influenza epidemic in Mexico City and indeed throughout the rest of the county. A total of 13 fatal cases of influenza were reported in Mexico City in the past three weeks. The Director at the National Center for Epidemiological Surveillance and Disease Control characterized the outbreak as “quite unusual.”

By 23 April Veratect had joined up the dots and yet the official international & national health organizations in America, Mexico or Canada had yet to go public.
Mexico had numerous humans cases of acute respiratory infections in Oaxaca, Distrito Federal (Mexico City), San Luis Potosí and Baja California involving several thousands of people.

All these Mexican regions were in close proximity to local airports with non-stop air links to southern states of the USA. Mexico City (Distrito Federal) airport connected via non-stop air traffic to many cities in the US, Canada, Europe and Latin America, with the most outbound traffic to Los Angeles, Frankfurt, Houston, Dallas and Amsterdam.
In the weeks prior to the ‘pig flu’ taking flight, Mexicans were also on the move in their millions! Semana Santa - April 3 – 12, Palm Sunday to Easter Sunday - is a traditional Mexican holiday period.  Mexico’s population is approximately 90% Catholic and a large proportion of its population moves around the country during this time period.

On 24 April (Friday) Mexico reports positive laboratory samples for ‘swine flu’ H1N1, a new viral pathogen of humans.  World media are now made aware of the situation in Mexico and CDC issues its first press statement, as does the World Health Organisation[2].

Dr DAVID OBENDORF

Reference:

[1] http://biosurveillance.typepad.com/biosurveillance/2009/04/swine-flu-in-mexico-timeline-of-events.html

[2] Influenza-like illness in the United States and Mexico

24 April 2009—The United States Government has 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. No deaths have been reported.

The Government of Mexico has reported three separate events. In the Federal District of Mexico, surveillance began picking up cases of ILI starting 18 March. The number of cases has risen steadily through April and as of 23 April there are now 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, have been reported. And from Mexicali, near the border with the United States, four cases of ILI, with no deaths, have been reported.
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.

The majority of these cases have 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 are of high concern.

Dr DAVID OBENDORF

All these Mexican regions were in close proximity to local airports with non-stop air links to southern states of the USA. Mexico City (Distrito Federal) airport connected via non-stop air traffic to many cities in the US, Canada, Europe and Latin America, with the most outbound traffic to Los Angeles, Frankfurt, Houston, Dallas and Amsterdam.  In the weeks prior to the ‘pig flu’ taking flight, Mexicans was also on the move in their millions! Semana Santa - April 3 – 12, Palm Sunday to Easter Sunday - is a traditional Mexican holiday period.  Mexico’s population is approximately 90% Catholic and a large proportion of its population moves around the country during this time period.