Since the initial reports of H1N1 influenza (human swine influenza; caused by influenza A/2009/H1N1/swl) in Mexico and the United States in mid April 2009, many thousands of cases have been reported worldwide. At the time of writing, community transmission is becoming established in many areas in Australia, but the number of reported cases is likely to be an underestimate of the true incidence due to policies for testing.

These guidelines provide advice to clinicians on the use of antiviral agents for this newly emerged influenza virus. A full version of these guidelines, including all references, has been previously published online (http://www.mja.com.au/public/rop/cheng/che10661_fm.html).

• In areas with established community transmission, patients presenting with an acute febrile respiratory illness (fever with cough and/or sore throat) are considered to have H1N1 influenza 09 and testing is generally not recommended.

• Early in the course of the pandemic, timely influenza diagnostic tests can be used to enable targeted antiviral treatment, but will be less useful once community transmission is widespread.

• Health care workers performing nose swabs or other high-risk aerosol-generating procedures (eg, suctioning, bronchoscopy or intubation) should use a particulate respirator (N95, P2 mask or equivalent), eye protection, impervious gowns, gloves, and, where possible, carry out the procedure in a negative pressure room.

• The use of nasopharyngeal aspirates are not recommended because of the risk to staff.

• The use of a combined nose–throat swab is recommended for diagnosis.

• Specimens for viral nucleic acid detection and culture at reference laboratories should be taken for epidemiological surveillance and to monitor for drug resistance. Once the pandemic is established, this is best facilitated through existing sentinel surveillance systems.

• Antiviral treatment has been shown to reduce the duration of symptoms and may also reduce the incidence of lower respiratory tract infection.

• Neuraminidase inhibitors (oseltamivir and zanamivir) are the antiviral agents of choice for H1N1 influenza 09.

• Dose recommendations for treatment and prophylaxis are provided in Box 1 and Box 2, respectively.

• The decision to treat an individual patient, particularly before the results of confirmatory testing are available, depends on three factors:

• An assessment of the likelihood of influenza, based on the known prevalence of infection in the region, a history of contact and the characteristics of the illness.

• An assessment of the likely benefits of treatment (Box 3), based on the presence of established complications, comorbidities and risk factors (Box 4), and the time since onset of the illness.

• The phase of the pandemic and the public health policies regarding distribution of the national stockpile (Box 5).

• Antiviral treatment should only be given to patients with confirmed or suspected influenza within 48 hours of symptom onset, except in cases of severe influenza.

• Treatment should be prioritised for patients with risk factors for poor outcomes, such as the morbidly obese, pregnant women, those with chronic disease (including asthma, cardiorespiratory disease, diabetes and renal failure) or immunosuppression, and those presenting with severe disease.

• Antiviral treatment can be given to children as young as 1 year.

• Parents should be warned of the possibility of rare neuropsychiatric symptoms related to oseltamivir use in children and adolescents.

• There is a concern regarding central nervous system accumulation of neuraminidase inhibitors in infants aged under 1 year, based on animal data; a treatment decision must balance the potential benefits of treatment with potential toxicity.

• Antiviral treatment should be offered to pregnant women with suspected or confirmed influenza because of the risk of severe disease in this group.

• Oseltamivir and zanamivir are in the Australian Drug Evaluation Committee category B1, with limited evidence suggesting safety.

• Antiviral treatment should be given to hospitalised patients with severe influenza infection (especially pneumonia), even if commenced more than 48 hours after the onset of symptoms.

• Antibiotic treatment should not be given routinely for influenza-like illness, but antibiotic treatment should follow established national guidelines for treatment of community-acquired pneumonia.

• Long-term prophylaxis can be given to first-responder health care workers for up to 6 weeks for oseltamivir and up to 4 weeks for zanamivir. Use of antiviral prophylaxis for these groups should be in the context of agreement to use the national stockpile.

• Antiviral prophylaxis can be given to health care workers and close contacts of patients with influenza following exposure, and to residents of institutions to terminate outbreaks.

• Contacts not provided with prophylaxis should have access to early treatment with antiviral agents, where indicated.

We acknowledge that the evidence on which these recommendations are based is rapidly changing. In particular, estimates of disease severity and case fatality, and risk factors for severity are poorly defined at present and may influence clinical decision making. We therefore include some resources for further information.

• Updates to these clinical guidelines will be posted on the websites of the Australasian Society for Infectious Diseases (ASID) (http://www.asid.net.au), the Thoracic Society of Australia and New Zealand (TSANZ) (http://www.thoracic.org.au) and the MJA (http://www.mja.com.au).

• Australian resources for pandemic influenza, including links to clinical and infection control guidelines (http://www.flupandemic.gov.au) and current information on the H1N1 outbreak (http://www.healthemergency.gov.au and http://www.influenza specialistgroup.org.au).

• For information on accessing personal protective equipment and antiviral medication, see links below:

• http://www.emergency.health.nsw.gov.au/swineflu/professionals/index.asp (New South Wales)

• http://humanswineflu.health.vic.gov.au/practitioners/index.htm (Victoria)

• http://www.health.qld.gov.au/swineflu/html/hc_resources.asp (Queensland)

• http://flu.sa.gov.au/Swineflu/InformationforGPs.aspx (South Australia)

• http://www.public.health.wa.gov.au/3/952/3/human_swine_flu_health_providers.pm (Western Australia)

• http://www.pandemic.tas.gov.au/what_does_it_mean_to_you/health_sector (Tasmania)

• http://www.health.nt.gov.au/H1N1_Influenza/General_Information_Resources/index.aspx (Northern Territory)

• http://health.act.gov.au/c/health?a=da&did=11044035&pid=1242181681 (Australian Capital Territory).