One year after the threat of an H1N1 pandemic, data gathered about influenza A  (H1N1) was presented Sunday during session A91 “H1N1 Pandemic Influenza, a Year Later: The Current State of Knowledge.”

Seven presentations addressed how data were collected and analyzed to determine which population groups were most threatened and which treatments worked best.

Summary of H1N1 in 2009

Looking back at the effect of the H1N1 virus in 2009, most of the illness was mild to moderate and most fatalities were among older patients, some of which may have been related to season flu.

That was the report of Tim Uyeki, M.D., M.P.H., M.P.P, of the Influenza Division of the Centers for Disease Control and Prevention in Atlanta, who presented “Summary of 2009 H1N1: Epiudemiology, Disease Impact, Antiviral Resistance and Diagnostic Performance.”

During the last flu season, 61 million cases of flu were reported, with 274,000 hospitalizations and 12,470 deaths, he said. By far, the greatest number of cases was in the over-65 age group. Other groups with the greatest number of cases reported were pregnant women, mostly in the second or third trimester, and the obese.

“Morbid obesity is coming out in studies as a risk factor ,” said Dr. Uyeki, who added that the morbid obese also appear to be at risk of contracting seasonal flu.

Other subgroups at risk for H1N1 were those with chronic pulmonary disease; chronic cardiac, renal and hepatic disease; immunosuppression; neuromuscular and neurocognitive conditions; and metabolic disease.

Gathering Data About H1N1

A vital part of combating H1N1 is the collection of data, which was addressed in “Clinical Learning at the Pace of Pandemics: The HHS 2009 H1N1 Critical Care Registry Experience,” presented by Lewis Rubinson, M.D., Ph.D., a senior medical advisor in the U.S. Department of Health and Human Services (HHS) Office of the Assistant Secretary for Preparedness and Response.

Dr. Rubinson detailed how the Department of HHS established an infrastructure to develop a data registry to help researchers, public health officials and clinicians develop a plan for the diagnosis and treatment of H1N1.

Looking at some of the preliminary data gathered about adults was B. Taylor Thompson, M.D., of Massachusetts General Hospital in Boston, who presented “2009 H1N1-Associated Critical Illness in Adults.”

Dr. Thompson reviewed data collected through the acute respiratory distress syndrome (ARDS) network. Among the data collected was a list of co-morbidities—led by hypertension, diabetes, asthma, COPD and congestive heart failure—and symptoms that led to hospitalization of H1N1 patients—led by cough, dyspnea and fever.

The summary of the data, she said, showed that multiple tests were needed to confirm the diagnosis and that respiratory failure caused 40 percent of all deaths. Also, about 20 percent of all patients were previously healthy and less than one-third were diagnosed with bacterial co-infection, Dr. Thompson said.

The data for children showed that older children and chronically ill children with compromised immune systems were at greatest risk from H1N1, which was reviewed in “2009 H1N1-Associated Critical Illness in Children,” presented by Adrienne G. Randolph, M.D., M.Sc., who is an associate professor at Harvard Medical School.

Dr. Randolph reviewed data about H1N1’s effect on children around the world, which showed that the five- to 12-year-old age group was at greatest risk, followed by the 13- to 17-year-old age group.

Patients with encephalitis or myocarditis had increased mortality in ARDS data collected. Among the conclusions from the data was that Staphylococcus aureus and vitamin D deficiency were major contributors to mortality in otherwise healthy children.

H1N1 Treatment

“Influenza Antiviral Drugs for Pandemic H1N1 Management,” presented by Frederick G. Hayden, M.D., who is a professor of medicine at the University of Virginia at Charlottesville, addressed the use of antiviral treatments for H1N1.

He addressed the effectiveness of antiviral agents, focusing on oseltamivir dosing considerations for the critically ill, the obese and infants. Also, it was found that early, empiric antivirals were especially important in treating patients with progressive illness, pneumonia, co-morbidities or pregnancy. Higher doses and longer regimens were also recommended.

H1N1 Prevention and Vaccination

“2009-H1N1: Prevention,” was presented by Richard J. Whitley, M.D., who is a professor in the Department of Medicine at the University of Alabama in Birmingham. He discussed approaches to controlling influenza, including vaccination, chemophrophylaxis and personal protective measures.

Research showed that a single dose of 2009 H1N1 vaccine was immunogenic in adults, with mild-to-moderate vaccine-associated reactions, he said. In addition, the monovalent 2009 influenza A (H1N1) MF59-adjuvanted vaccine generates antibody responses that are likely to be associated with protection after a single dose is administered.

William Busse, M.D., who is a professor medicine at the University of Wisconsin, discussed the success in vaccination against H1N1 among asthma patients in his presentation, “The NIAD-NHLBI H1N1 Study in Asthma.”

Dr. Busse reviewed the NHLBI Severe Asthma Research Program (SARP), which was used to determine how severe asthma differentiated patients from those with non-severe asthma. Patients were classified as having severe asthma if they used oral corticosteroids for more than six of the last 12 months, had corticosteroid injections for more than six of the last 12 months and had a high dose of inhaled corticosteroids for more than 10 of the last 12 months.

The study concluded that one dose of H1N1 vaccine provides seroprotection in most asthma patients and that in severe asthma, the single dose provided the lowest level of seroprotection among older subjects, he said.

In addition, there were no differences in seroprotection between severe versus mild or moderate asthma, Dr. Busse said.