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Diagnosis |
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There are no pathognomic signs and symptoms ofH5N 1 infections. The
clinical, laboratory, and radiological findings are not distinguishable from
other causes of influenza-like illness, severe community acquired pneumonia
or ARDS. The only feature that raises the suspicion of avian influenza
infection is the epidemiological linkage to endemic areas and the history of
contact with poultry. The frondine clinicians should therefore always try to
elicit a detailed history of travel and exposure to animals in suspected
patients. Those with a positive travel or contact history should receive
appropriate radiological and microbiological investigations, together with
proper infection control precautions. Patients with mild influenza-like
illness may be isolated and closely observed while waiting for results of
laboratory investigations. A chest radiograph should be performed to exclude
pulmonary involvement. The decision for hospitalisation is based on a
clinical assessment of disease severity, whether the patient can be readily
followed up, and the likelihood of having avian influenza infection. Those
with severe pneumonia and risk factors for avian influenza should initially
be empirically treated with oseltamivir (Antiflu) in addition to
broad-spectrum antibiotics (eg,
B-Iactam plus a macrolide). |
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Which drugs are available for
treatment? |
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Two drugs (in the neuraminidase inhibitors
class), oseltamivir (Antiflu) and zanamivir can reduce the severity and
duration of illness caused by seasonal influenza. The efficacy of the
neuraminidase inhibitors depends, among others, on their early
administration (within 48 hours after symptom onset). For cases of human
infection with H5N1, the drugs may improve prospects of survival, if
administered early, but clinical data are limited. The H5Nl virus is
expected to be susceptible to the neuraminidase inhibitors.
So far, most instances of fatal pneumonia
seen in cases of H5Nl infection have resulted from the effects of the virus,
and cannot be treated with antibiotics. Nonetheless, since influenza is
often complicated by secondary bacterial infection of the lungs, antibiotics
could be lifesaving in the case of late-onset pneumonia. WHO regards it as
prudent for countries to ensure adequate supplies of antibiotics in advance.
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How effective is oseltamivir (Antiflu)?
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Limited evidence suggests that some antiviral
drugs, notably oseltamivir (Antiflu), can reduce the duration of viral
replication and improve prospects of survival, provided it is administered
within 48 hours following symptom onset. However, prior to the outbreak in
Turkey, most patients have been detected and treated late in the course of
illness. For this reason, clinical data on the effectiveness of oseltamivir
are limited. Moreover, oseltamivir and other antiviral drugs were developed
for the treatment and prophylaxis of seasonal influenza, which is a less
severe disease associated with less prolonged viral replication.
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When should oseltamivir (Antiflu)
therapy be initiated? |
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In suspected cases, Antiflu should be
prescribed as soon as possible (ideally, within 48 hours following symptom
onset) to maximize its therapeutic benefits. However, given the significant
mortality currently associated with H5N 1 infection and evidence of prolonged
viral replication in this disease, administration of the drug should also be
considered in patients presenting later in the course of illness.
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What is the dose of Antiflu? |
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The recommended dose of Antiflu for the
treatment of influenza, in adults and adolescents 13 years of age and older,
is 150 mg per day, given as 75 mg twice a day for 5 days. The recommended
oral dose of Antiflu for prophylaxis of influenza in adults and adolescents
13 years and older following close contact with an infected individual is 75
mg once daily for at least 10 days. Safety and efficacy have been
demonstrated for up to 6 weeks. Oseltamivir is not indicated for the
treatment of children younger than 1 year of age. Dose adjustment is
required in patients with renal impairment.
As the
duration of viral replication may be prolonged in cases ofH5N 1 infection,
clinicians should consider increasing the duration of treatment to 7-10 days
in patients who are not showing a clinical response. In cases of severe
infection with the H5Nl virus, clinicians may
need to consider increasing the recommended daily dose or the duration of
treatment, keeping in mind that doses above 300 mg per day are associated
with increased side effects. For all treated patients, consideration should
be given to taking serial clinical samples for later assay to monitor
changes in viral load, and to assess drug susceptibility and drug levels. These samples should be
taken only in the presence of appropriate measures for infection control.
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What are the side effects of
oseltamivir (Antiflu)?
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The most
frequently reported events with oseltamivir are nausea, vomiting, diarrhoea
and dizziness In severely ill H5N1 patients or in H5N1
patients with severe gastrointestinal symptoms, drug absorption may be
impaired. This possibility should be considered when managing these
patients. |
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What about zanamivir?
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Zanamivir is an orally inhaled powdered drug
that is approved for the treatment of influenza in patients aged 7 years and
older. The dose is 10 mg twice daily |
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What is the status of vaccine
development and production?
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Vaccines effective against a pandemic virus
are not yet available. Vaccines are produced each year for seasonal
influenza but will not protect against pandemic influenza. Although a
vaccine against the H5N1 virus is under development in several countries, no
vaccine is ready for commercial production and no vaccines are expected to
be widely available until several months after the start of a pandemic. Further reading 1. www.cdc.gov/flu 2. www.who.int/csr/disease/avian_influenza/en/
3. Chest 2006; 129: 156-168 |
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