The Dept of Anaesthesia & Intensive Care, CUHK
Pascale Gruber, Charles Gomersall, Gavin Joynt
First posted 224th April 2006
This page is based on: Gruber PC, Gomersall CD, Joynt GM. Avian influenza (H5N1): implications for intensive care, published in Intensive Care Medicine. Reproduced here, in part, with the permission of Springer Verlag. Click here to download the published version (requires subscription).
The clinical features of fever, lower respiratory tract symptoms, headache, myalgia, diarrhea, vomiting, abdominal and chest pain, coma and bleeding from mucosal membranes are too non-specific for a clinical diagnosis to be made. History of exposure to birds should be sought. Interestingly, secondary bacterial infection appears uncommon . Manifestations of H5N1 are often severe with 41 of the 65 reported cases (63%, 95% CI: 51-75%) requiring advanced organ support [3,11,12,14,16-24]. However, reported cases may represent only the severe end of the spectrum as there is evidence of asymptomatic and mild infection [4,25]. Details of patients requiring advanced organ support are given in table 1. Important points to note are:
Twenty two of the 41 cases who required advanced organ support (54%) developed ARDS but this is likely to be an underestimate. Many patients with severe respiratory failure were reported with insufficient detail to establish whether they had ARDS. Pneumothorax was common (17%). All pneumothoraces occurred during mechanical ventilation.
Typical laboratory findings :
Detection of viral RNA in respiratory samples appears to offer the greatest sensitivity for early identification of avian (H5N1) flu. Unlike human influenza virus, H5N1 is associated with a higher frequency of virus detection in pharyngeal than in nasal samples .
Diagnosis can be confirmed by one or more of the following:
Commercial rapid antigen tests may help provide support for a diagnosis of influenza A infection but have a poor negative predictive value and lack specificity for H5N1
Neuraminidase inhibitors (oseltamivir and zanamivir) specifically target one of two surface structures of influenza virus, the neuraminidase protein. The presently circulating genotype Z of the avian influenza H5N1 virus carries mutations in the M2 gene and is therefore resistant to adamantanes (amantadine and rimanadine).
Current guidelines recommend that oseltamivir should be administered within 48 hours at a dose of 75mg twice daily for five days in adults, with weight adjusted doses for children. In more severe cases higher doses and a longer course of therapy has been recommended . The efficacy of neuramidase inhibitors diminishes substantially if administered after 60 hours of infection and efficacy suboptimal when instituted later in the course of illness. However antiviral treatment could still be of benefit if there is ongoing viral replication .
At present there are no data to support the use of steroids or other immunomodulatory agents in H5N1 infections .
Prevention & prophylaxis
No influenza (H5) vaccines are currently commercially available for human use. Although vaccination against human influenza A is unlikely to protect against avian influenza it does reduce the risk of concurrent infection with both viruses, which may lead to an exchange in genetic material between human and avian viruses, resulting in a reassorted transmissible pandemic virus . Chemoprophylaxis with oseltamivir 75 mg daily for 7-10 days is warranted for persons who have had a possible unprotected exposure .
April, 2014 unless
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