Lessons Learned from 2009 H1N1 Influenza Pandemic

Although the H1N1 influenza pandemic of 2009-2010 proved, overall, to be no more severe than seasonal H3N2, it provided some valuable lessons with respect to special populations and treatment.

Cameron Wolfe, MD, MBBS, Duke Preparedness & Response Center, Division of Infectious Diseases, Durham, NC, provided a thorough overview of the lessons learned from the pandemic during his presentation "The Co-evolution of Infection Control and Antibiotic-resistant Pathogens," which was the Edward H. Cass lecture at this year's annual meeting of the Infectious DIseases Society of America.

In addressing the issue of severity of illness, he noted that there was an overrepresentation of indigenous groups in North America, the Pacific and Australia, and a significant overrepresentation of African Americans. "This is something that does need to be investigated," Wolfe said. Further, the risk of severe or fatal disease was increased by 5 to 15 times in obese individuals. A high risk for hospitalization and death was also associated with pregnant women and prepartum mothers.

Vaccination

Wolfe said that vaccination of hospital staff proved a massive controversy during the pandemic, but this is an issue of protection for staff. "For us, there was no stronger message I could give my administrators than what happened on one of our wards: four patients developed H275Y in identical sequence and they all subsequently died. They were in immediately adjacent rooms," Wolfe said. "We know the vaccine is safe with 0.8 cases of Guillain-Barre Syndrome per million cases. There really should be very little reason not to vaccinate."

Pharmacotherapy

The neuraminidase inhibitor Oseltamivir is deemed first-line therapy, and inhaled zanamivir the alternative in that class of drugs. According to Wolfe, the M2-ion channel blockers amantadine and rimantidine almost exclusively are not effective against pHINI and most H5N1. "Most people do not need treatment, they are 'well outpatients' " Wolfe said. However this does not apply for the sick and high risk patients. In the critically ill, five days of treatment may not be sufficient; it can be extended to 10 days, especially in the immunocompromised.

Regarding prophylaxis, it can be appropriate in immune-compromised patients. Drug resistance is extremely rare. Combination therapy could result in changing resistance, and there is variable efficacy and a lack of primary data with any of the treatment options, Wolfe said.

He also touched on salvage strategies, and steroids in particular. A meta-analysis from 2009 shows benefit in acute respiratory distress syndrome (ARDS) morbidity/mortality, however no benefit was seen in studies done in Hong Kong, Thailand and Vietnam in H5N1 mortality. Steroids may provide benefit in cases of septic shock and adrenal insufficiency. "The evidence that steroids are helpful is far from proven," Wolfe said. "There's a range of other salvage modalities, none of which have proven benefit over the other."

Extracorporeal Membrane Oxygenation (ECMO)

Wolfe said that ECMO “bypasses the lungs, giving patients time to recover," and is a proven modality for severe respiratory failure in neonates. "The CESAR trial (2009) in the UK became a real game-changer. It was stopped early at 180 patients -- they had planned for 300 -- because a selective survival advantage was seen in patients receiving ECMO, Wolfe said.

"ECMO is here to stay," he said. However, it should always be coupled with other lung protective strategies. And, better ECMO outcomes are evident in viral ARDS compared with younger, healthier patients.