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Swine-Origin Influenza A (H1N1) and HIV

The CDC offers guidance for HIV-infected patients potentially exposed to swine flu.

During the past several weeks, human infections with a novel strain of swine-origin influenza A (H1N1) have been identified in the U.S., Mexico, and more than a dozen other countries. In response, the WHO has set the pandemic alert level to 5 on a 6-point scale, indicating human-to-human transmission of this virus in at least two countries within one WHO region and signaling a high likelihood of an imminent pandemic. The clinical presentation of swine-origin influenza is not different than that of seasonal influenza (high fever, cough, sore throat, rhinorrhea, and malaise), although there seems to be a higher proportion of patients presenting with diarrhea and abdominal pain. Many HIV-infected individuals and their providers are understandably concerned about the risks of H1N1 infection. On April 30, the CDC issued interim guidance on this particular issue.

At this point, sufficient data are not available to determine whether HIV-infected individuals are at increased risk for complications of H1N1 infection. Dr. Sierra-Madero has been actively calling HIV providers in Mexico City and has yet to hear of any cases of influenza A (H1N1) among HIV-infected patients during the current outbreak. Limited evidence from seasonal influenza studies indicates that influenza may be no more severe for most HIV-infected individuals than for healthy, HIV-negative individuals. Nevertheless, clinicians should be aware that HIV-infected individuals who acquire H1N1 infection — especially those with AIDS or low CD4-cell counts — may be at increased risk for more severe disease and complications. In addition, they may be at increased risk for secondary bacterial infections, including pneumonia.

The currently circulating strain of H1N1 virus is sensitive to the neuraminidase inhibitors zanamivir and oseltamivir but is resistant to the adamantanes amantadine and rimantadine (JW Infect Dis 2009 Apr 29). The CDC’s core recommendations for treatment and chemoprophylaxis in HIV-infected adults are the same as those for other populations at increased risk for complications from influenza:

• HIV-infected adults and adolescents who meet current case definitions for confirmed, probable, or suspected H1N1 infection should receive empiric antiviral treatment.
  
• HIV-infected adults and adolescents who are close contacts of persons with probable or confirmed H1N1 infection should receive antiviral chemoprophylaxis.
  
• HIV-infected adolescents and adults who are household contacts of a suspected case can consider antiviral chemoprophylaxis.
  
• Oseltamivir and zanamivir treatment and chemoprophylaxis regimens recommended for HIV-infected persons are the same as those recommended for HIV-negative adults with seasonal influenza.
  
• There are no known contraindications for coadministration of oseltamivir or zanamivir with currently available antiretroviral medications.
  

Comment: Clinicians should keep in mind the possibility of prolonged drug-resistant influenza virus infection occurring in immunosupressed individuals with lymphocytopenia (J Infect Dis 2009;199:1435).

Although a reasonable estimate of the effectiveness of influenza vaccination for HIV-infected individuals cannot be made conclusively, a meta-analysis (HIV Med 2008; 9:57) suggests that it is around 50%; thus, it is prudent to immunize all HIV-infected persons against seasonal influenza each year. The ACIP recommends routine influenza vaccination for HIV-infected individuals; however, recent data indicate that vaccination rates remain low (J Infect Dis 2007; 196:339). Ongoing general information on the H1N1 epidemic can be found at http://www.pandemicflu.gov.

— Carlos del Rio, MD, and Juan Sierra-Madero, MD

Dr. Sierra-Madero is Director of the AIDS Clinic at Instituto Nacional de La Nutricion "Salvador Zubiran" in Mexico City.

Published in Journal Watch HIV/AIDS Clinical Care May 4, 2009

Citation(s):

Centers for Disease Control and Prevention (CDC). Interim guidance—HIV-infected adults and adolescents: Considerations for clinicians regarding swine-origin influenza A (H1N1) virus. Updated April 30 , 2009, 12:45 PM ET. (http://www.cdc.gov/h1n1flu/guidance_HIV.htm).

Reader Remarks:

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