Reports of outbreaks among humans in in the U.S. and internationally have increased.
-- A new multi-species form of influenza that combines swine, avian and human viruses has been spreading between humans in Texas and in California, causing the Centers for Disease Control and Prevention (CDC) to launch an investigation.
"We don't know whether this virus or any other virus will lead to the next pandemic," Dr. Richard Besser, acting director of the CDC, said during a press briefing April 24. He stressed that there is not enough information about the spread and source of the viruses to gauge the health risk at this time.
The viruses detected in the eight people infected in the United States, who range in age from 9 to 52, included genetic pieces from the North American swine influenza A virus (H1N), North American avian influenza viruses, human influenza viruses, and swine influenza viruses found in Asia and Europe. The combination is one never seen before in the United States or elsewhere, reports Dr. Anne Schuchat, director of CDC's National Center for Immunization and Respiratory Diseases.
Three new possible cases had surfaced as of April 25 -- two in Kansas and one in New York -- but the CDC has yet to confirm that they are the new flu virus combination.
Of greater concern is the number of cases being reported in Mexico, which has now confirmed several cases, one possibly ending in death, Besser said April 24. CDC said April 23 during a press briefing that no other cases outside the United States had been reported, and Besser says the new revelation has caused the CDC's concern about the outbreak to grow. International health organizations are on the watch, too, for the outbreak to possibly reach pandemic status.
Of the 14 samples sent to the CDC April 24 from Mexico, seven were positive for the viruses similar to those that infected people in California and Texas, he says.
The World Health Organization also is tracking the outbreak, and says 12 cases with viruses identical to the outbreaks in Texas and California have been reported in Mexico, plus another 18 cases of traditional swine influenza. Additionally, 854 cases of pneumonia are being reported in Mexico City, 59 of those cases resulting in death. In central Mexico, 24 cases of a flu-like outbreak have been reported, with three deaths, plus four cases resulting in no deaths reported in Mexicali, an area that is spread along the Mexico/California border.
Peculiarly, none of the infected people in the United States came into contact with swine, Schuchat said during a media briefing April 23.
The CDC has tracked an average of about one case of human infection of swine influenza every one or two years, with a total of 12 since 2005. Swine influenza infections in humans are rare, though, and have previously occurred in humans who had contact with infected pigs. One case in Wisconsin in 1988 indicated human-to-human spread from an initial infected person whose health care workers later became infected with flu-like symptoms and displayed antibody evidence of swine flu infection, according to the CDC.
The most recent cases involve infection between a daughter and father pair in California and two teenage boys who were schoolmates in Texas. All the cases have centered along the Mexican border.
Besser says CDC is sending investigation teams to California, Texas and Mexico to expand its investigation.
Household members of the seven people infected displayed flu-like symptoms around the same time as the infected persons, but no specimens were collected from them, so Schuchat says it's impossible to tell if they also were infected with the same virus.
At this point, the CDC does not know the extent of the spread of this particular strain of influenza, how the people came to be infected with it, or why it is spreading from person to person. But Schuchat says "we don't think this is a time for major concern around the country. But we want you to know what we're doing."
Besser announced April 24 that the CDC would issue an outbreak notice to travelers heading to central Mexico and Mexico City. They won't need to take special precautions, he says, adding the notice is just a reminder of good travel policies like washing hands frequently and seeing one's doctor for any flu-like symptoms.
All the people in the reported U.S. cases have recovered, but the viruses have proved resistant to amantadine and rimantadine anti-viral drugs. They are, however, susceptible to oseltamivir and zanamivir, both newer anti-viral drugs for flu.
Symptoms of the new strain are similar to regular flu symptoms, like fever cough and sore throat. But Schuchat says this strain is presenting with more vomiting and diarrhea than regular flu. The viruses cannot be spread through eating pork, she adds. Those infected will show symptoms within 9 days or so, and be contagious for up to 7 days.
Clinicians and other health professionals who may be in contact with the viruses are asked to send samples to the CDC for additional investigation.
Schuchat says she expects more cases will come to light as a result of the investigation and says CDC findings will be updated daily on its Web site.