Who's at High Risk From Swine Flu?

New Flu Riskiest for Pregnant Women, Kids Under 5 or With Asthma, Many Others

Medically Reviewed by Louise Chang, MD on July 21, 2009

July 21, 2009 -- A pregnant Florida woman who got swine flu, lost her baby, and now fights for her life has drawn media attention to the fact that pandemic flu isn't just "moderately severe" for everybody.

Aubrey Opdyke, who came down with swine flu while pregnant, was placed in a medically induced coma on June 3. Doctors last week tried to deliver her baby prematurely, but the infant did not survive. Opdyke remains in intensive care.

A similar case is reported from Australia. Early in the pandemic, on May 12, the CDC reported details of three cases of swine flu in pregnant women. One of the women, age 33, died two days after giving birth to a healthy child. The other two women received Tamiflu treatment; they and their babies are doing well.

The word is now out: Pregnant women are at increased risk of complications from pandemic swine flu. But they aren't the only people at higher risk.

Underlying Medical Conditions and Swine Flu

Flu viruses attack the upper and lower airways, making it harder for a person to breathe. That's one of the reasons the flu is such a miserable illness even for people who were healthy when they caught the flu bug.

But anyone with an underlying illness that can make breathing difficult is at much greater risk from the flu. Flu can send someone with a chronic lung condition -- such as asthma or COPD -- to a hospital equipped with mechanical ventilators.

The flu also makes a person's lungs more susceptible to bacterial infection. With seasonal flu, bacterial infections are a leading cause of flu deaths. Those most vulnerable to such flu complications are adults over 65 -- especially those in nursing homes -- and kids under 2.

Just like seasonal flu, pandemic swine flu is hard on elderly people. But so far in the current pandemic, relatively few elderly people are getting the disease. It's mostly striking younger people.

Kids under 5 have been at higher risk of swine flu complications. Those with asthma are, of course, at particularly high risk. So are kids with medical conditions -- such as diabetes -- that put adults at higher risk from flu.

One group of children and teens faces an unusual risk: those under age 19 who must take long-term aspirin therapy. Aspirin is a dangerous drug for people who have the flu, as it raises a person's risk of a dangerous complication called Reye's syndrome.

Adults at 'Higher Risk' From Swine Flu

As noted above, pregnancy, lung diseases, and older age put adults at higher risk of swine flu complications.

Those aren't the only underlying medical conditions that make swine flu dangerous. Here's the rest of the list:

  • Cardiovascular conditions (except high blood pressure)
  • Liver problems
  • Kidney problems
  • Blood disorders, including sickle-cell disease
  • Neurologic disorders
  • Neuromuscular disorders
  • Metabolic disorders, including diabetes
  • Immune suppression, including HIV infection and medications that suppress the immune system
  • Residency in a nursing home or other chronic-care facility

A striking number of adults who developed severe swine flu complications have been morbidly obese. However, obesity itself does not seem to be the issue. The vast majority of extremely obese people suffer respiratory problems and/or diabetes, which seem to be the underlying reason for severe flu complications.

Why Do Some People Suffer Severe Swine Flu?

Many of the people who have suffered severe complications of swine flu -- including death -- have not been in any of the risk groups. Alarmingly, some have been apparently healthy young people.

One reason for this is simply statistical. Because the first wave of the swine flu pandemic has spread most explosively in schools, young people have been exposed in disproportionate numbers. Because more young people are infected, more of the severe cases (as well as more of the mild cases) occur in this population.

Another reason may have to do with the virus. While the pandemic 2009 H1N1 bug does not seem to carry any of the flu genes linked to extreme virulence, it does more readily infect lung tissues than the seasonal flu bugs now in circulation.

Ferret studies suggest that the pandemic swine flu bug isn't yet fully adapted to humans because it doesn't spread easily in small sneeze and cough droplets. That's a good thing, because small droplets carry the virus deep into the lungs. This may be why the swine flu causes relatively few severe flu cases, despite the virus's ability to home in on lung tissue.

A third reason may have to do with immunity. The seasonal flu vaccine doesn't protect against the type A H1N1 swine flu, even though it immunizes against a seasonal type A H1N1 virus. But people who have had multiple vaccinations, or who once were infected with an H1N1 virus, might mount a better immune response to swine flu than younger people with less exposure to vaccine and/or flu.

And there's evidence that people born before 1957 -- when an ancestor of the swine flu bug was in seasonal circulation -- might have some degree of protection against swine flu.

But there's no definitive answer to why some people suffer worse flu disease than others. The best course for everyone is to avoid infection when healthy and to avoid infecting others when sick.

Show Sources


Morbidity and Mortality Weekly Report, May 15, 2009; vol 58: pp 497-500.

Maines, T.R. Sciencexpress, July 2, 2009.

CDC, Health Alert Network: "Three Reports of Oseltamivir Resistant Novel Influenza A (H1N1 Viruses," July 9, 2009.

CDC: "Interim Guidance for Novel H1N1 Flu (Swine Flu): Taking Care of a Sick Person in Your Home," July 8, 2009.

CDC: "Interim Guidance -- HIV-Infected Adults and Adolescents: Considerations for Clinicians Regarding Novel Influenza A (H1N1) Virus," June 5, 2009.

CDC: "Pregnant Women and Novel Influenza A (H1N1) Virus: Considerations for Clinicians," June 30, 2009.

CNN: "Baby Delivered Prematurely From Swine Flu Patient Dies," July 20, 2009.

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