The respiratory tract is one of the most common sites for infections as it comes into contact with pathogens frequently.  Influenza A and B viruses and RSV are collectively responsible for a majority of respiratory illnesses and cause significant morbidity and mortality.^{1'' 2'' 3'' 4}

Infections with Influenza A and B viruses often result in the respiratory illness commonly referred to as the ‘flu.’ Flu is highly contagious'' and'' according to the CDC'' 5-20% of the population contract the flu each year. Over 200''000 people are hospitalized'' and between 3''000 and 49''000 people die of complications each year'' depending on the severity of the season.⁵ Symptoms include fever'' cough'' headache'' body aches'' congestion'' and fatigue. Flu can lead to serious complications such as pneumonia'' bronchitis'' sinus infections'' and a general worsening of chronic conditions.⁶

In the spring of 2009 a novel quadruple-reassortant virus'' now known as 2009 H1N1 Influenza'' emerged in North America and quickly spread'' becoming a global pandemic by the summer of 2009.⁷ According to CDC estimates'' the virus infected between 43 million and 89 million people between April 2009 and April 2010.⁸ Importantly'' this Influenza A subtype was found to be largely susceptible to the antiviral drug oseltamivir (brand name Tamiflu)''⁹ while antiviral resistance varied among other Influenza A subtypes.¹⁰ Thus'' treatment decisions may be impacted by the timely availability of Influenza A subtyping information.

During the 2007-08 flu season'' certain isolates of influenza A (subtype H1N1) were found to be resistant to oseltamivir.¹¹ Resistance was conferred by a histidine to tyrosine substitution in the neuraminidase active site (H275Y in N1 nomenclature).¹² The same H275Y resistance mechanism has also been identified in 2009 H1N1 strains.^13''14

Respiratory Syncytial Virus (RSV) infection is the most common cause of bronchiolitis and pneumonia in children under 1 year of age in the United States.  Each year 75''000 to 125''000 children in this age group are hospitalized due to RSV infection.  Symptoms of RSV infection include coughing'' sneezing'' runny nose'' fever'' and decrease in appetite. RSV is also recognized as a serious contributor to respiratory ailments in the aged and Immunocompromised demographic. Flu and RSV occur as seasonal outbreaks in the United States'' generally starting as early as October or November and ending as late as April or May.^{5'' 15}

References

1. Thompson'' W.W.'' Shay'' D.K.; Weintrau'' E.'' et. al. Mortality associated with influenza and respiratory syncytial virus in the United States. JAMA 2003; 289; 179-186.
2. Jansen'' A.G.S.C.'' Sanders'' E.A.M.'' Hoes'' A.W.'' et. al. Influenza- and respiratory syncytial virus-associated mortality and hospitalizations. Eur. Respir. J. 2007; 30; 1158-1166.
3. Falsey'' A.R.'' Hennessey'' P.A.'' Formica'' M.A.'' et. al. Respiratory syncytial virus infection in elderly and high-risk adults. New Engl. J. Med. 2005; 352; 1749-1759.
4. Mahoney'' J. B. Detection of Respiratory Viruses by Molecular Methods. Clin. Microbiol. Rev. 2008; 21; 716-747.
5. “Q&A: Seasonal Influenza (Flu): The Disease''” Centers for Disease Control and Prevention. Updated September 10'' 2010. Retrieved October 22'' 2010 from http://www.cdc.gov/flu/about/qa/disease.htm
6. “Seasonal Influenza (Flu) – Flu Symptoms & Severity''” Centers for Disease Control and Prevention. Updated September 8'' 2010. Retrieved October 22'' 2010 from http://www.cdc.gov/flu/about/disease/symptoms.htm
7.  “The 2009 H1N1 Pandemic Summary Highlights'' April 2009-April 2010''” Centers for Disease Control and Prevention. Updated August 3'' 2010. Retrieved October 29'' 2010 from http://www.cdc.gov/h1n1flu/cdcresponse.htm
8. “CDC Estimates of 2009 H1N1 Influenza Cases'' Hospitalizations and Deaths''” Centers for Disease Control and Prevention. Updated May 14'' 2010. Retrieved October 29'' 2010 from http://www.cdc.gov/h1n1flu/estimates_2009_h1n1.htm
9. “Key Facts About Antiviral Drugs and Influenza (Flu)''” Centers for Disease Control and Prevention. Updated September 9'' 2009. Retrieved October 29'' 2010 from http://www.cdc.gov/flu/protect/antiviral/keyfacts.htm
10. Centers for Disease Control and Prevention. 2008. Update: Influenza Activity—United States'' September 28-November 29'' 2008. Respiratory Syncytial Virus Activity – United States'' July 2008-December 2009. MMWR 57(49): 1329-1332.
11. Euro Surveill'' 2008. Emergence of resistance to oseltamivir among influenza A(H1N1) viruses in Europe. Euro Surveill 2008; 13(5). Available online: http://www.eurosurveillance.org/edition/v13n05/080131 2.asp.
12. Carr M.J.'' Sayre N.'' Duffy M.'' et. al. Rapid molecular detection of the H275Y oseltamivir resistance gene mutation in circulating influenza A (H1N1) viruses. J Virol Methods. 2008; 153; 257-262.
13. Gaur A.H.'' Bagga B.'' Barman S.'' et. al. Intravenous zanamivir for oseltamivir-resistant 2009 H1N1 influenza. New Engl. J. Med. 2010; 362; 88-89.
14. Mai L.Q.'' Wertheim H.F.'' Duong T.N.'' et. al. A community cluster of oseltamivir-resistant cases of 2009 H1N1 influenza. New Engl. J. Med. 2010; 362; 86-87.
15. “RSV: Frequently Asked Questions''” Centers for Disease Control and Prevention. Updated October 17'' 2008. Retrieved October 22'' 2010 from http://www.cdc.gov/rsv/about/faq.html