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CDC swine flu update
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Source: CDC
In a press briefing on May 18, Dr. Ann Schuchat from the Immunization and Respiratory Center of the CDC reported 22 states around the country with widespread and regional swine flu (A/H1N1) activity. “Unfortunately, based on the trends we're seeing, we do expect more illness, more hospitalizations and more deaths.
While Florida has as many as 103 confirmed cases, there are no deaths here. Dr. Schuchat reported 6 deaths in the US including a recent one in a school principal in New York City.
“We are now experiencing higher levels of influenza-like illness than is normal for this time of year, including numerous outbreaks in schools, which is also very unusual.” She went on to say that because influenza viruses are unpredictable, it is still uncertain how severe this outbreak will be in terms of the ultimate illness and mortality toll or whether this strain will turn out to be worse than previous strains.
“Things could change quickly, and we do continue our efforts to prepare, particularly for the fall, where history tells us we might have a second wave of this new virus.”
As of May 19, the official case counts are a total of 5,123 cases throughout the U.S. There is some geographic variation in the H1N1 flu activity, with highest activity currently in the Pacific Northwest and the Southwest.
“These cases, however, are just what we call the tip of the iceberg,” Dr. Schuchat said. “We're also seeing more reports of influenza-like illness from our monitored outpatient visits than would be typical for this time of year. There have been over 200 hospitalizations, and 6 fatalities.” According to Dr. Schuchat, current cases including those hospitalized are primarily in younger people between ages 5 and 24. “Unlike the seasonal flu, we're seeing relatively few cases or hospitalizations in people over 65. That's a very different feature that seems to be holding up through our surveillance.”
Although the data so far shows that people under 18 are more likely to have infection when another person in the family is infected, it is not tonally clear why. “What we call age-specific attack rates in the households suggest a difference in transmission to younger people versus older people,” Dr. Schuchat said. “From the literature describing other infectious diseases and from some infectious disease modeling, we believe children are very good at transmitting infectious diseases. They have lots of social contacts, and in particular, younger children may shed the virus for a longer time. We are looking at virtual shedding in some of the field investigations, but I don't have those data yet.”
In terms of why older people seem less likely to become ill with the swine flu, Dr. Schuchat said that, though still not confirmed through laboratory testing, one of the working hypotheses is that older adults may have some preexisting protection against this virus due to previous exposure to some other somewhat related virus. An alternate hypothesis is that it just may take longer for this virus to make its way into the senior population.
Dr. Schuchat tried to stress the fact that numbers of cases are less important than patterns. The map shown here can also be viewed on the CDC website where it is constantly updated and indicates which states have widespread disease or regional disease. While half of the cases tested have been seasonal influenza, the other half have been swine flu or what is now being called a novel H1N1 virus.
In response to questions about whether the swine flu virus is changing or causing more disease, Dr. Schuchat said that so far there no evidence of any mutation toward a more virulent strain. However, she added that the CDC would continue to track the virus to determine any changes including resistance to treatment.
“We do think that the way the virus is spreading in the U.S. we are not out of the woods, and disease is continuing. Our CDC efforts continue fairly aggressively,” There are more than 80 people deployed in the field, and the CDC continues to support laboratories and states in the U.S., as well as in countries shipping their diagnostic kits to 95 labs in 50 states, and to 237 labs in 107 countries. At this point, 40 of the states in the U.S. have validated testing going on.
In terms of vaccine development, Dr. Schuchat said since it takes months before a vaccine could be available once it goes into production, the CDC and others are already working on making a candidate virus that could be turned over to manufacturing for production.
To questions about whether W.H.O. will change their phase 5 classification to a phase 6 which would mean that the virus is spreading in a sustained way in at least two regions of the world, Dr. Schuchat said that a decision has not been officially made.
“It's important to know that we're seeing sustained spread in the U.S., she said. “We need to continue to be vigilant as we look towards the summer in the Southern hemisphere and the fall back here in the U.S.
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