FLU NEWS FROM ICAAC: H1N1 studies, IV peramivir findings, Tamiflu for H5N1

Sep 14, 2009 (CIDRAP News) – A wide range of research findings on pandemic H1N1 influenza, seasonal flu, and avian flu was presented over the weekend at the 49th annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) in San Francisco (www.icaac.org).

Triple antiviral therapy better than single drugs
A triple combination therapy comprising three flu antiviral drugs—amantadine, oseltamivir (Tamiflu), and ribavirin—controls replication of flu viruses better than any of those drugs used independently, according to a multi-national team. Researchers from Adamas Pharmaceuticals in California, Utah State University, the Naval Health Research Center of San Diego, the University of Alabama, and Amsterdam Medical Center in the Netherlands tested the drugs alone and in combination in vitro against H1N1 flu viruses and also against seasonal flu strains that were resistant to amantadine and oseltamivir. (Nguyen JT, et al: "In vitro activity of triple combination therapy against drug-resistant influenza viruses.")

Rapid flu tests miss H1N1 cases
Rapid tests may not detect novel H1N1 flu as well as slower, more expensive molecular tests do, raising the possibility of under-counting and missed diagnoses, according to researchers from the University of South Florida College of Medicine and Tampa General Hospital. The team took tested samples from suspected flu patients using a rapid test and a polymerase chain reaction (PCR) test, and compared both results with a second test by the Florida Department of Health. Sixty-six patients tested positive for influenza A at the Department of Health, but the in-hospital PCR detected only 48 of them and the rapid test only 18. The rapid test also returned 18 false-positives. (Montero JA, et al: "Discordance between a rapid antigen test and PCR for detection of influenza in the current setting of an evolving pandemic of novel H1N1.")

Link between immunoglobulin levels and H1N1 severity seen
The results of a study from three institutions in Melbourne, Australia, suggest that administering immunoglobulin to patients with severe H1N1 infection may mitigate the impact of the disease, particularly in pregnant women who appear to be more vulnerable. The group assessed levels of total serum immunoglobulin as well as particular immunoglobulin subclasses in patients with moderate H1N1 infection and in those with severe cases requiring intensive care, some of whom were pregnant, as well as in uninfected pregnant women. They found that pregnant women infected with H1N1 were more likely to have lower levels of immunoglobulin, and that levels were lower in severe cases than in mild ones. (Gordon CL: "Association between severe swine-origin influenza A virus [S-OIV] infection and immunoglobulin G2 subclass deficiency.")

MRSA as fatal complication in H1N1 cases
Bacterial co-infections should be considered a dangerous complication of H1N1 infection, researchers from the Women's and Children's Hospital of Buffalo, N.Y., and two other institutions warned. The group described severe infections in a 9-year-old girl and a 15-year-old boy who arrived at the emergency room several days after being seen for mild flu symptoms. Both children died of necrotizing pneumonia caused by infection with methicillin-resistant Staphylococcus aureus (MRSA) as a secondary complication of H1N1 flu. (Johnson KK, et al: "Two fatal pediatric cases of pandemic H1N1/09 influenza complicated by community-acquired methicillin-resistant Staphylococcus aureus [CA-MRSA]")

IV peramivir compares well with Tamiflu for seasonal flu
A single intravenous (IV) dose of the experimental antiviral drug peramivir worked as well as a course of oral oseltamivir (Tamiflu) in a study in Asia, according to an Associated Press (AP) report from the ICAAC meeting. Flu patients were given either a single IV dose of peramivir (300 or 600 mg) or 5 days of oseltamivir, the AP reported. Symptoms cleared in 78 or 81 hours with the lower and higher doses of peramivir, respectively, and in 82 hours with oseltamivir, the story said. Dr. Shigeru Kohno of Nagasaki University, the lead researcher, said side effects were less common with peramivir. But flu expert Dr. Fred Hayden noted that many patients last winter had oseltamivir-resistant strains of flu.

Oseltamivir improves survival in H5N1 and seasonal flu
Roche, maker of Tamiflu, reported two retrospective studies indicating that the drug significantly improved survival rates in H5N1 avian flu and seasonal flu patients. In the analysis of avian flu cases, 11 of 89 patients (12%) who did not receive the drug survived, versus 45 of 85 (53%) of those who received at least one dose up to 8 days after falling ill. The study is described as the first to systematically assess human H5N1 cases in multiple countries. The other study was an analysis of 760 patients in Hong Kong who had severe seasonal flu, half of whom received oseltamivir. The mortality rates were 6.0% in the untreated group compared with 3.8% in the treated group, a 37% reduction, according to Roche.
[Sep 13 Roche press release]

H1N1 described as all-ages infection
Compared with seasonal flu, H1N1 flu causes more infections in teenagers and adults and is also responsible for more intensive care unit (ICU) admissions, according to an analysis by the Toronto Invasive Bacterial Diseases Network. A comparison of the clinical features and outcomes of 154 seasonal flu infections in the 2007-08 flu season, along with the first 158 H1N1 infections in the Toronto region, showed that H1N1 infections were more evenly distributed across age-groups and were more likely to occur in children and adults with underlying conditions. (Rebbapragada A, et al: "A comparison of clinical features and outcomes of hospitalization due to seasonal and pandemic influenza A [H1N1].")

Severe H1N1 cases in children
Although H1N1 infection is often mild, 16% of 80 children admitted to a Montreal children's hospital in May and June required ICU care, 13% were experiencing seizures or other neurologic symptoms at admission, and 35% had abnormally low oxygen levels on arrival. One child died. Two-thirds of the children had underlying conditions—asthma, sickle-cell disease, encephalopathy, and others— that may have predisposed them to illness, said researchers at the Ste. Justine Hospital Research Centre. (Laumay E, et al: "Novel influenza A [H1N1] related hospitalization in a pediatric tertiary care centre: who's at risk for severe disease?")

News editor Robert Roos contributed to this report.

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