H1N1 influenza swine flu pandemic virus causes severe lung failure in young people who are healthy otherwise, studies suggest.
Severe respiratory failure in healthier youths is seen as quite specific to H1N1 strain, which is not associated with the attack of any of the other flu virus strains since the 1918 flu that killed millions of people, according to studies published in the Journal of the American Medical Association.
“H1N1 can produce rapidly progressive respiratory failure,” wrote Douglas White and Derek Angus, professors of critical care medicine at University of Pittsburgh School of Medicine, in Pittsburgh, in an editorial.
H1N1 infection develops rather rapidly causing severe illnesses in younger people often leading them to intensive care units, according to the published studies of outbreaks in Canada and Mexico.
H1N1 influenza virus has been found more lethal in youngsters leading to severe illness and death, in earlier studies as well.
To date, most severe H1N1 infections and deaths have occurred in adults under the age of 50 years.H1N1 deaths in the elderly comparatively rare. This is true for those most frequently infected, and especially so for those experiencing severe or fatal illness.
Severe respiratory failure, the most reported cause of death due to H1N1 pandemic infection are also in young and otherwise healthy people.In these patients, the virus directly infects the lung, causing severe respiratory failure. This is very peculiar to H1N1 pandemic and is rarely seen during seasonal influenza.
Highly specialized and demanding care in intensive care units, usually with long and costly stays is often required to save these lives.
Several countries, during the winter season in the southern hemisphere, have viewed the need for intensive care as the greatest burden on health services. Some cities in these countries report that nearly 15 percent of hospitalized cases have required intensive care.
A higher risk of hospitalization and death is also found among certain subgroups, including minority groups and indigenous populations. The risk in these groups is four to five times higher than in the general population, studies show.
Certain medical conditions notably asthma, cardiovascular disease, diabetes and immunosuppression also increase the risk of severe and fatal illness. Worldwide, more than 230 million people suffer from asthma, and more than 220 million people are estimated to have diabetes.
An increased risk during pregnancy is now consistently well-documented across countries.This risk takes on added significance for a virus, like H1N1, that preferentially infects younger people.
The hospitalization rate for pregnant H1N1 patients is more than four times that of the general population, a study last month in the medical journal Lancet found.
About 6% of the deaths in the United States from H1N1 virus have been pregnant women. Some of these women have had other chronic conditions, though pregnancy, particularly in the third trimester is known to make it harder to recover from respiratory infections.
Pregnant women may be more vulnerable to swine flu because of the failure of the immune system to figh the infection, according to Australian doctors said.
Obesity is another condition leading to the fatality due to H1N1 infection.
Why the H1N1 strain becomes more aggressive with the young is not fully understood. Researchers, however, suggest that the H1 component, a subtype of the virus protein hemagglutinin, in both swine flu and human flu has a common ancestor.
H1 circulated in humans, evolving continuously during the 1918 and 1957 influenza pandemics. H1 then became inactive, replaced by other subtypes of hemagglutinin such as H3. H1 in humans reappeared in 1977 and has been a dominant subtype of human flu ever since.
Even though H1 has evolved significantly from 1977 to the present in humans, the H1 has evolved very little in pigs. Swine flu H1 has been very similar to the “original” 1918 and 1930 versions of H1.
So, it is assumed that most people born before 1957 were exposed to human H1 influenza. Their immune systems produced antibodies to Old H1. Since Old H1 has not been seen in humans in many years, younger people do not have antibodies to make them immune to old H1 which is very close to 2009 A/H1N1 swine flu.
Nearly 4,500 people have died worldwide from swine flu.