The type A seasonal flu virus (a subtype of the H1N1 strain) appears to be developing increasing restistance to the most widely used flu drug in the US, Tamiflu (generic name oseltamivir). For the first time, type A viruses were starting to show increased resistance to Tamiflu in the 2007-2008 flu season, but this year the resistance is higher and more widespread.
These are the findings of a study that has been published early online in Journal of the American Medical Association, JAMA because of its public health importance said a press release from the publisher.
The study was the work of Dr Nila J. Dharan, of the Centers for Disease Control and Prevention (CDC), Atlanta, and colleagues who looked at trends and characteristics of patients infected with H1N1 type A Tamiflu-resistant and susceptible flu.
The viruses were tested as part of ongoing surveillance and were identified and submitted to the CDC between September 2007 and May 2008, and then a year later, between 28 September 2008 and 19 February 2009.
The researchers found that during the 2007-2008 flu season, the H1N1 type A flu strains accounted for about 19 per cent of circulating flu strains in the US. Of the 1,155 US H1N1 type A viruses tested during that season, 142 of them (12 per cent) showed resistance to Tamiflu (oseltamivir).
From that period (2007-2008) the researchers found data was available for 99 people infected with Tamiflu-resistant and 182 people infected with Tamiflu-susceptible flu. For the resistant cases the median (the midpoint of the range) age was 19, while 5 patients ended up in hospital and 4 died.
On analyzing the demographic, illness and symptom characteristics available on the infected people, the researchers found no significant differences between those infected with Tamiflu-resistant and those infected with Tamiflu-susceptible flu strains and neither did they find any links between use of Tamiflu and flu cases due to infection with H1N1 type A in the US.
The data on the current flu season, 2008-2009 is obviously not complete since the season is not yet finished, but an analysis on that which has been gathered so far shows that Tamiflu resistance in H1N1 type A strains continue at a high level. Up to 19 February 2009, Tamiflu resistance was found in 264 of 268 (98.5 per cent) of the H1N1 type A viruses tested by the CDC.
The authors wrote that:
“The emergence of oseltamivir resistance has highlighted the need for the development of new antiviral drugs and rapid diagnostic tests that determine viral subtype or resistance, as well as improved representativeness and timeliness of national influenza surveillance for antiviral resistance.”
In December last year the CDC issued draft guidelines for the use of antiviral flu medications in line with what they found after analyzing the data coming in for the current season. They recommended that doctors and other health professionals:
“Consider the results of patient testing and local influenza surveillance data on circulating types and subtypes of influenza viruses in deciding whether oseltamivir [tamiflu] alone could be used. These guidelines provide options, including preferential use of [the anti-viral drug] zanamivir or a combination of oseltamivir and [the anti-viral drug] rimantadine, which might be more appropriate in treating patients who might have influenza caused by an oseltamivir-resistant virus.”
In an accompanying editorial, Dr David M. Weinstock of the Dana-Farber Cancer Institute, Boston, and Dr Gianna Zuccotti of Brigham and Women’s Hospital, Boston, who is also Contributing Editor, JAMA, Chicago, wrote:
“The understanding of influenza biology and epidemiology has advanced markedly; however, the global dissemination of oseltamivir [Tamiflu]- resistant influenza came as a great surprise.”
There is no doubt that further new susprises will occur in the “perpetual struggle with influenza” they warn, since the one thing we all know for sure is that the organism will evolve and at a pace that we need to outstrip with faster diagnosis down to identifying speciments at the molecular level, with extensive surveillance among humans and animals, and, they add:
“More rapid and [flexible] systems for translating basic and epidemiological discoveries into clinically applicable interventions.”
But for now, our best defence is the tried and tested foursome:
“Vaccination, social distancing, hand washing, and common sense,” they wrote.
“Infections With Oseltamivir-Resistant Influenza A(H1N1) Virus in the United States.”
Nila J. Dharan; Larisa V. Gubareva; John J. Meyer; Margaret Okomo-Adhiambo; Reginald C. McClinton; Steven A. Marshall; Kirsten St. George; Scott Epperson; Lynnette Brammer; Alexander I. Klimov; Joseph S. Bresee; Alicia M. Fry; for the Oseltamivir-Resistance Working Group.
JAMA. 2009;301(10).
doi:10.1001/jama.2009.294.
Early Release Article, posted March 2, 2009
Sources: JAMA Archives press release, journal article and editorial.
Written by: Catharine Paddock, PhD