Gert van der Hoek
In Memoriam - Editor, Senior Moderator
From Weekly Update:
Antiviral Resistance:
Since October 1, 2008, 1,148 seasonal influenza A (H1N1), 261 influenza A (H3N2), 654 influenza B, and 574 2009 influenza A (H1N1) virus isolates have been tested for resistance to the neuraminidase inhibitors (oseltamivir and zanamivir).
In addition, 798 2009 influenza A (H1N1) original clinical samples were tested for a single known mutation in the virus that confers oseltamivir resistance. Also, 1,153 seasonal influenza A (H1N1), 261 influenza A (H3N2), and 526 2009 influenza A (H1N1) viruses have been tested for resistance to the adamantanes (amantadine and rimantadine).
Additional laboratories perform antiviral testing and report their results to CDC. Two additional oseltamivir resistant 2009 influenza A (H1N1) viruses have been identified by these laboratories. The results of antiviral resistance testing performed on these viruses are summarized in the table below.
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Resistant viruses
2009 Influenza A (H1N1) number :1,678 9†‡ (0.6 %)
†Two screening tools were used to determine oseltamivir resistance: sequence analysis of viral genes or a neuraminidase inhibition assay.
‡Additional laboratories perform antiviral resistance testing and report their results to CDC. Two additional oseltamivir resistant 2009 influenza A (H1N1) viruses have been identified by these laboratories, bringing the total number to 11.
2009 influenza A (H1N1) viruses were tested for oseltamivir resistance by a neuraminidase inhibition assay and/or detection of genetic sequence mutation, depending on the type of specimen tested.
Original clinical samples were examined for a single known mutation in the virus that confers oseltamivir resistance in currently circulating seasonal influenza A (H1N1) viruses, while influenza virus isolates were tested using a neuraminidase inhibition assay that determines the presence or absence of neuraminidase inhibitor resistance, followed by the neuraminidase gene sequence analysis of resistant viruses.
The majority of 2009 influenza A (H1N1) viruses are susceptible to the neuraminidase inhibitor antiviral medication oseltamivir; however, rare sporadic cases of oseltamivir resistant 2009 influenza A (H1N1) viruses have been detected worldwide, including 11 cases in the United States.
All tested viruses retain their sensitivity to the other neuraminidase inhibitor: zanamivir.
Ten patients (including the nine viruses detected at CDC and one identified by an additional laboratory) had documented exposure to oseltamivir through either treatment or chemoprophylaxis, and the remaining patient is currently under investigation to determine exposure to oseltamivir.
Occasional development of oseltamivir resistance during treatment or prophylaxis is not unexpected. Enhanced surveillance is expected to detect additional cases of oseltamivir resistant 2009 influenza A (H1N1) viruses, and such cases will be investigated to assess the spread of resistant strains in the community.
To prevent the spread of antiviral resistant virus strains, CDC reminds clinicians and the public of the need to continue hand and cough hygiene measures for the duration of any symptoms of influenza http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5832a3.htm
Additional information on antiviral recommendations for treatment and chemoprophylaxis of influenza virus infection is available at (http://www.cdc.gov/h1n1flu/recommendations.htm) Antiviral treatment with oseltamivir or zanamivir is recommended for all patients with confirmed or suspected influenza virus infection who are hospitalized or who are at higher risk for influenza complications.
Three seasonal influenza A (H1N1) viruses collected between February 8 and May 11, 2009, were found to be resistant to both oseltamivir and the adamantanes (amantadine and rimantadine). All seasonal influenza A (H1N1) viruses tested retain their sensitivity to zanamivir.
The three dually-resistant viruses represent less than 1% of all seasonal influenza A (H1N1) viruses tested during the 2008-09 influenza season, and as a result, no changes to the influenza antiviral treatment or prophylaxis recommendations will be made at this time. CDC will continue to monitor trends in antiviral resistance over the summer and throughout the upcoming 2009-10 influenza season.
http://www.cdc.gov/flu/weekly/
Antiviral Resistance:
Since October 1, 2008, 1,148 seasonal influenza A (H1N1), 261 influenza A (H3N2), 654 influenza B, and 574 2009 influenza A (H1N1) virus isolates have been tested for resistance to the neuraminidase inhibitors (oseltamivir and zanamivir).
In addition, 798 2009 influenza A (H1N1) original clinical samples were tested for a single known mutation in the virus that confers oseltamivir resistance. Also, 1,153 seasonal influenza A (H1N1), 261 influenza A (H3N2), and 526 2009 influenza A (H1N1) viruses have been tested for resistance to the adamantanes (amantadine and rimantadine).
Additional laboratories perform antiviral testing and report their results to CDC. Two additional oseltamivir resistant 2009 influenza A (H1N1) viruses have been identified by these laboratories. The results of antiviral resistance testing performed on these viruses are summarized in the table below.
- snipped -
Resistant viruses
2009 Influenza A (H1N1) number :1,678 9†‡ (0.6 %)
†Two screening tools were used to determine oseltamivir resistance: sequence analysis of viral genes or a neuraminidase inhibition assay.
‡Additional laboratories perform antiviral resistance testing and report their results to CDC. Two additional oseltamivir resistant 2009 influenza A (H1N1) viruses have been identified by these laboratories, bringing the total number to 11.
2009 influenza A (H1N1) viruses were tested for oseltamivir resistance by a neuraminidase inhibition assay and/or detection of genetic sequence mutation, depending on the type of specimen tested.
Original clinical samples were examined for a single known mutation in the virus that confers oseltamivir resistance in currently circulating seasonal influenza A (H1N1) viruses, while influenza virus isolates were tested using a neuraminidase inhibition assay that determines the presence or absence of neuraminidase inhibitor resistance, followed by the neuraminidase gene sequence analysis of resistant viruses.
The majority of 2009 influenza A (H1N1) viruses are susceptible to the neuraminidase inhibitor antiviral medication oseltamivir; however, rare sporadic cases of oseltamivir resistant 2009 influenza A (H1N1) viruses have been detected worldwide, including 11 cases in the United States.
All tested viruses retain their sensitivity to the other neuraminidase inhibitor: zanamivir.
Ten patients (including the nine viruses detected at CDC and one identified by an additional laboratory) had documented exposure to oseltamivir through either treatment or chemoprophylaxis, and the remaining patient is currently under investigation to determine exposure to oseltamivir.
Occasional development of oseltamivir resistance during treatment or prophylaxis is not unexpected. Enhanced surveillance is expected to detect additional cases of oseltamivir resistant 2009 influenza A (H1N1) viruses, and such cases will be investigated to assess the spread of resistant strains in the community.
To prevent the spread of antiviral resistant virus strains, CDC reminds clinicians and the public of the need to continue hand and cough hygiene measures for the duration of any symptoms of influenza http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5832a3.htm
Additional information on antiviral recommendations for treatment and chemoprophylaxis of influenza virus infection is available at (http://www.cdc.gov/h1n1flu/recommendations.htm) Antiviral treatment with oseltamivir or zanamivir is recommended for all patients with confirmed or suspected influenza virus infection who are hospitalized or who are at higher risk for influenza complications.
Three seasonal influenza A (H1N1) viruses collected between February 8 and May 11, 2009, were found to be resistant to both oseltamivir and the adamantanes (amantadine and rimantadine). All seasonal influenza A (H1N1) viruses tested retain their sensitivity to zanamivir.
The three dually-resistant viruses represent less than 1% of all seasonal influenza A (H1N1) viruses tested during the 2008-09 influenza season, and as a result, no changes to the influenza antiviral treatment or prophylaxis recommendations will be made at this time. CDC will continue to monitor trends in antiviral resistance over the summer and throughout the upcoming 2009-10 influenza season.
http://www.cdc.gov/flu/weekly/