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Two studies, which are available online as early release articles and will be published in the November edition of the Journal of the American Medical Association (JAMA), detail the characteristics, treatment and outcomes of critically ill patients with H1N1 in Mexico and Canada [1-2].
Although the death rate in each of the studies is quite different, it nonetheless is as high or higher than that of seasonal flu. Furthermore, although seasonal flu typically affects people of older age — the average annual rate of influenza-associated hospitalizations over the last 20 years for people age 65 and older is 70%  — these studies show that H1N1 is striking many who are much younger. In both studies, the majority of critically ill patients with influenza A H1N1 had rapidly progressive respiratory failure and required mechanical ventilation.
Critically ill patients with influenza A H1N1 in Mexico
The first observational study was of 58 critically ill patients with H1N1 at 6 hospitals in Mexico . These patients accounted for 6.5% of 899 admitted to the hospital with confirmed, probable or suspected influenza A H1N1 between the months of March 24, 2009 and June 1, 2009. The patients had a median age of 44, just over half were female (53%) and 2 were healthcare workers. Two patients were children (10 and 14 years old). Only two patients had received a seasonal influenza vaccination in 2008 or 2009.
Patients developed symptoms a median of 6 days prior to hospitalization. Symptoms included fever, respiratory issues (cough, shortness of breath or wheezing), generalized weakness, muscle pain, headache and gastrointestinal symptoms of nausea, vomiting, or diarrhea. Additional disorders the patients presented with included obesity (36.2%), a past history of smoking (34.5%), hypertension (25.9%), diabetes type 1 or 2 (17.2%) and gastrointestinal disease (10.3%). The time from hospitalization to intensive care unit (ICU) admission was between 0 and 3 days. Almost all patients were treated with antibiotics; 78% received antiviral drugs (neuraminidase inhibitors); 69% received corticosteroids. Fifty-four of the 58 patients (93%), including one child, required mechanical ventilation during the course of hospitalization.
After 60 days from the onset of critical illness, 24 of the 58 (41%) had died. Most died within the first 2 weeks. The median age of patients who died was 39. All deaths within 28 days were primarily related to respiratory failure, with only one late death primarily related to multisystem organ dysfunction. Both children survived.
Critically ill patients with influenza A H1N1 in Canada
The second observational study was of 215 critically ill patients with confirmed, probable or suspected influenza A H1N1 at 38 study intensive care units in Canada . Since patients that had confirmed or probable H1N1 infection were significantly younger, had a longer duration of mechanical ventilation and ICU stay, and higher mortality than those with suspected disease, the analysis was restricted to the 168 patients that had confirmed or probable influenza A H1N1 infection. The patients had an average age of 32.3, 67.3% were female, and 30% were children. Only 10 of the 168 patients (6%) had received a seasonal influenza vaccination in the past two years.
Patients developed symptoms a median of 4 days prior to hospitalization. The most common symptoms included fever, respiratory issues, weakness and muscle pain. Possible bacterial pneumonia was present in just over 54 patients (30%). Additional disorders the patients presented with included chronic lung disease (including asthma, COPD and bronchopulmonary dysplasia; 41.1%), obesity (33.3%), hypertension (24.4%), a past history of smoking (22.6%) and diabetes type 1 or 2 (20.8%). The time from hospitalization to intensive care unit administration was between 0 and 2 days.
Almost all patients were treated with antibiotics; 90.5% received antiviral drugs (neuraminidase inhibitors); 50.6% received corticosteroids. Mechanical ventilation was used in 81% of patients on the first day of ICU admission. Clinical evidence for bacterial pneumonia following ICU admission was found in almost one-quarter of patients (41 of 168).
After 90 days from the onset of critical illness, 29 of the 168 (17.3%) had died. Eighteen patients died within the first 2 weeks and 24 died within 28 days from the onset of critical illness. The median age of patients who died was 42. The primary reported causes of death included severe respiratory failure, secondary infection and sepsis (generalized invasion of the body by pathogenic microorganisms or their toxins), and multiorgan dysfunction.
What to expect
An accompanying editorial in the JAMA issue said that although both studies have substantial epidemiological limitations, they nonetheless :
… provide important signals about what clinicians and hospitals may confront in the coming months. H1N1 can produce a rapidly progressive respiratory failure that is refractory to conventional mechanical ventilation, often in young, healthy patients — a group who are not currently a priority group for H1N1 vaccination.
You can protect yourself from the H1N1 virus as well as the seasonal flu:
- Get the H1N1 vaccine and the seasonal flu vaccine.
- Wash your hands often or use alcohol-based hand cleaner.
- Don’t cover your nose and mouth with you hand when you cough or sneeze! Use a tissue instead and throw it in the trash after use.
- Avoid touching your eyes, nose or mouth — these are areas where the virus can enter your body.
- Avoid sick people.
- Get lost of rest, eat well and drink plenty of fluids.
- If you do get sick, stay home.
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- Dominguez-Cherit et al. Critically Ill Patients With 2009 Influenza A(H1N1) in Mexico. JAMA. 2009 Oct 12. [Epub ahead of print]
- Kumar et al. Critically Ill Patients With 2009 Influenza A(H1N1) Infection in Canada. JAMA. 2009 Oct 12. [Epub ahead of print]
- Thompson et al. Influenza-associated hospitalizations in the United States. JAMA. 2004 Sep 15;292(11):1333-40.
- White and Angus. Preparing for the Sickest Patients With 2009 Influenza A(H1N1). JAMA. 2009 Oct 12. [Epub ahead of print]