Viral Influenza Complications
Abstract & Commentary
By Joseph F. John, MD, FACP, FIDSA, FSHEA, Associate Chief of Staff for Education, Ralph H. Johnson Veterans Administration Medical Center; Professor of Medicine, Medical University of South Carolina, Charleston, SC, is Associate Editor for Infectious Disease Alert.
Dr. John is a consultant for Cubist, Genzyme, and bioMerieux, and is on the speaker's bureau for Cubist, GSK, Merck, Bayer, and Wyeth.
Source: Rothberg MB, et al. Complications of viral influenza. Am J Med. 2008;121:258-264.
Clinicians are becoming more attuned to the many complications of influenza, particularly with the high morbidity and mortality seen with H5N1 strains spreading around the world. The infectious disease group from Baystate Medical Center in Springfield, MA, has done a good job compiling a modern article on complications of influenza. They organized their summary into several sections.
Risk stratification. The emphasis here is on older age, immunosuppression either endogenously with HIV infection or through organ transplantation. Allograft rejection may be associated with influenza infection
Pulmonary complications. These complications fall into four categories:
• Primary influenza virus pneumonia. Up to 18% of patients admitted to the hospital with pneumonia may fall into this group. With H5N1 infection, after an incubation of 3-8 days, symptoms may become extremely severe.
• Secondary bacterial pneumonia. Most readers know about the dreaded superinfections with staphylococci and the pneumococcus. Toxic shock may be a byproduct of infection with S. aureus associated with influenza. With the national epidemic of community MRSA, that can cause necrotizing pneumonitis itself, clinicians have to be especially wary of progression of disease due to CoMRSA.
• Infection with unusual pathogens. The pathogens that we usually do not think about but which can superinfect the flu victim are group B streptococci, Legionella pneumophila, and even Aspergillus sp.
• Exacerbations of COPD. The mechanism of this complication is poorly understood but treating the underlying influenza infection may forestall this process.
Miscellaneous complications. The most notable of other complications include psychiatric manifestations which have not been well studied, central nervous system involvement that should be documented with CSF analysis, CNS involvement caused by Reye's Syndrome, a non-inflammatory brain process associated with liver failure, and myositis severe enough to produce rhabdomyolysis, probably more common with influenza B.
Vaccine and antiviral medications. Rothberg and colleagues stress here the use of vaccine as the "cornerstone" of prevention of influenza illness but there is not adequacy of data to say that complications are reduced. For that reason, Rothberg et al stress that during an influenza outbreak, viral entry blockers like amantadine and rimantadine along with two neuraminidase inhibitors, oseltamivir and zanamivir, are options for reducing complications. There are many issues of resistance with both classes of antivirals, and we know very little because of the lack of clinical trials, about the true efficacy of these medications in avian influenza.
Commentary
This year has been a tricky one for influenza. The "match" for vaccine versus infection types was not good, so when the final analysis of influenza cases is complete this summer, we are likely to see this has been a difficult year with influenza. As of April 5th, CDC published data have shown that of 34,380 isolates from the United States, only 6.1% were H1 types, 16.3% H3 types, and 51.6% unsubtyped A types. Almost 26% were influenza B viruses. The CDE weekly web site has further information: http://www.cdc.gov/flu/weekly.
New vaccine formulations for the 2008-2009 season will include the Brisbane viruses and B/Florida. The formulation is changed for all three components from the 2007-2008 formulation. Depending on the actual make-up of the unsubtyped viruses, we may see again that the vaccine may not be a good match. According to the CDC web site information, the A/Brisbane H1N1 component represents a recent genetic variant evolved from the A/Solomon Islands/03/2006 virus. The H3N2 A/Brisbane which constituted 71% of 161 H3N2 virus typed by the CDC is a recent antigenic variant from A/Wisconsin/67/2005-like viruses.
Regarding the complications of influenza discussed by Rothberg et al in this article, they suggest that the more novel the infecting virus, for example, H5N1, the more likely may be complications. The pathogenesis of H5N1 may be somewhat unusual. Spread of the H5N1 virus beyond the lung has been suggested, but severe symptoms may relate more to cytokine disregulation (Emerg Infect Dis. 2005;11:1036-1041). Thus, the amount of systemic symptoms and signs present may vary with the novelty of the virus. The high mortality rate being seen with circulating H5N1 isolates continues to be high and of great concern.
Clinicians need to be every wary about the evolution of influenza viruses. Pandemic influenza programs currently envelop our health care institutions; however, there is no way to know when or if we will see pandemic influenza soon. The more subtle changes in both influenza A and B viruses and the sporadic impact of H5N1 strains remain enough of a challenge for health care providers from this season to the next.
Clinicians are becoming more attuned to the many complications of influenza, particularly with the high morbidity and mortality seen with H5N1 strains spreading around the world.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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