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Ordinarily this headline would be met with smirks and admonitions of "Don't drink the water!"  But it is glaringly apparent that in Mexico, a virus of some sort has caused hospitalizations and deaths. 

From the Canadian Press:

Doctors warned to watch for mystery illness in tourists returning from Mexico

TORONTO — Public health units, quarantine officers and medical practitioners across the country have been warned to be on guard for cases of a mystery illness in Canadians returning from Mexico.

The warning follows reports from that country of cases of severe respiratory illness, which in some cases has led to death.

Mexican authorities have insisted the outbreak is not an epidemic and that preventive measures are being taken to reduce the risk of transmission of disease.

Mexican authorities informed Canadian counterparts about the situation on April 17, asking for help with their investigation. Scientists at the National Microbiology Laboratory in Winnipeg are assisting in efforts to determine the cause or causes of the illnesses.

"We are aware of the reports and are looking into them," said Andrew McDermott, a spokesperson for the Public Health Agency of Canada.

It's not clear if there is any link between these illnesses and the recent discovery of several human cases of swine flu infection in California. (bold mine)

Dr. Arlene King, who is the Public Health Agency of Canada's point person for pandemic influenza preparedness, said samples from Mexico will need to be studied to see if there is any link.

King, who was named Ontario's new chief public health officer on Thursday and takes on the job in mid-June, said it is important to be on the lookout for new infectious disease outbreaks.

"We absolutely have to remain vigilant in the country around the situation in Mexico and globally," said King, who is director general of the public health agency's centre for immunization and respiratory infectious diseases.

"We need to be prepared for any emerging infectious disease threat that may occur outside of our borders. It's absolutely fundamental."

A spokesperson for the Pan American Health Organization - the World Health Organization's Americas branch - said PAHO is also working with Mexican authorities to look into the reports.

"We're co-operating with (Mexican) authorities on it," Donna Eberwine-Villagran said from Washington.

"We have people in our field office in Mexico City and also in our border office working with Mexican authorities looking at the cases."

The illnesses are said to have been occurring in south and central Mexico and involve mainly young, previously healthy adults. Some reports have suggested health-care workers have become ill.

To date, two clusters of severe respiratory infections with death have been reported in April, one in Mexico City and one in San Luis Potosi. Mexico City has reported 120 cases including 13 deaths while San Luis Potosi, in central Mexico, has reported 14 cases including four deaths. (bold mine)

In addition there has been a death reported in Oaxaca, in southern Mexico and two deaths reported in Baja California Norte, which borders California.

Health authorities have been told some of the cases have tested positive for influenza, but some cases are influenza A and others are influenza B.

A leading infectious diseases expert said a number of pathogens could be the culprit or culprits.

"It could be anything," said Dr. Allison McGeer of Toronto's Mount Sinai Hospital. "Full range from new and unidentified virus to stuff that goes on every day and somebody just did a test."

She added, though that it was "improbable" that the illness was being caused by anything exotic and was most likely the work of influenza or an adenovirus. (bold mine)

An advisory from Toronto Public Health to health professionals said that given the severity of the illness, health care workers should be actively looking for cases of severe respiratory infection in people who have been in Mexico in the previous two weeks.

But the advisory stressed that there is no evidence the infections are caused by an unusual pathogen or a novel flu strain.

Mexican health officials held a news conference Wednesday to discuss the situation, putting the surge in illnesses down to end-of-season flu activity.

Mauricio Hernandez Avila, the undersecretary for health prevention and promotion, said the health department had initiated an active search for cases of serious pneumonia associated with the illness in the country, especially in the federal district that encompasses Mexico City.

Copyright © 2009 The Canadian Press. All rights reserved.

The pattern of cases to deaths looks similar to what the pacific Northwest saw with its most recent documented outbreak of Adenovirus 14, or Ad14 for short.  A ten to twenty-five percent CFR (Case fatality Rate) in hospitalized patients would mirror the findings in the Seattle study, which can be found in great detail on this Blogsite (keyword search: adenovirus).

Of course, a 10% CFR is also reminiscent of SARS, but it is highly doubtful that SARS would have skipped oceans and continents and found its way to Mexico.

Likewise, influenza is just not a killer in these numbers, even swine flu.  So my vote is good old Ad14, and the sooner the CDC starts testing for it, the sooner we all will find that is our latest "silent epidemic" and then someone can set about finding a vaccine for Ad14 and other flavors of adenovirus.