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Study: Quantifying H1N1 Risk Factors

 

 

# 4419

 

From almost the start of the pandemic of 2009 we heard warnings and anecdotal stories about specific risk factors that predisposed some people towards hospital and/or ICU admissions when stricken by the H1N1 swine flu virus.

 

In late May, weeks before the pandemic was officially declared, I posted the following list from the CDC of those believed to be at higher risk from this, and other, influenza viruses.

 

 

Groups at Higher Risk for Severe Illness from Novel Influenza A (H1N1) Infection

Groups of people at higher risk for severe illness from novel influenza A (H1N1) infection are thought to be the same as those people at higher risk for severe illness from seasonal influenza. These groups include:

  • Children younger than 5 years old
  • Persons aged 65 years or older
  • Children and adolescents (younger than 18 years) who are receiving long-term aspirin therapy and who might be at risk for experiencing Reye syndrome after influenza virus infection
  • Pregnant women
  • Adults and children who have pulmonary, including asthma, cardiovascular, hepatic, hematological, neurologic, neuromuscular, or metabolic disorders such as diabetes
  • Adults and children who have immunosuppression (including immunosuppression caused by medications or by HIV)
  • Residents of nursing homes and other chronic-care facilities.

 

Pregnancy was an important risk factor in the 1918 Spanish Flu, and again during the 1957 pandemic, so concerns over it (and other risk factors) formed the basis for a good deal of discussion over the summer.  A few examples include:

 

Pregnancy & Flu: A Bad Combination

WHO Pandemic Briefing # 5: Influenza In Pregnant Women
Lancet Study: Pregnancy And H1N1

 

 

While it may take years before we understand – with any precision – the full impact of this pandemic, we are seeing more post-pandemic-wave analyses being published, such as this one from PLoS Currents Influenza entitled:

 

 

Preliminary estimation of risk factors for admission to intensive care units and for death in patients infected with A(H1N1)2009 influenza virus, France, 2009-2010

To estimate the magnitude of the risks associated with age, obesity, pregnancy and diabetes, we compared the prevalence of these conditions reported in hospitalized severe cases to that in the general population, during the 2009-2010 A(H1N1) pandemic flu in France.

 

Pregnancy, obesity, heart failure and diabetes were risk factors for admission into an intensive care unit (OR=5.2 [95%CI 4.0-6.9], 3.8 [3.0-4.9], 3.3 [2.6-4.1] and 2.8 [2.3-3.4], respectively).

 

Only heart failure, obesity, and diabetes were significantly associated with death (OR=6.9 [4.9-9.8], 3.6 [1.9-6.2], and 3.5 [2.5-5.1], respectively). Elderly adults were at lower risk of being admitted into an ICU, but at higher risk of death.

 

 

A word of caution. 

 

This study looked at five specific risk groups; age, diabetes, pregnancy, obesity, and heart failure and not at the full gamut of H1N1 hospitalization risk factors.  

 

You’ll find no mention of Asthma, COPD, or Neuro/ Developmental disorders – all of which have been linked to higher rates of H1N1 hospitalization in other studies.

 

And so this data must be viewed in that limited context.

 

Over time, studies such as this one – when combined with dozens of others – will help us understand how the pandemic of 2009 affected the world.    

 

Some of the other hospitalization studies we’ve seen over the past few months include:

 

CDC Q&A On H1N1 And Underlying Conditions
CMAJ: Asthma As A Pandemic Risk Factor In Children
Australian Study: H1N1 Hospitalized Patients
Study: H1N1 Hospitalization Profiles
Study: H1N1 A Threat To All Age Groups

 

No doubt we’ll see dozens more over the coming months. 

Related Post:

Pandemic
PLoS

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