Emergencies preparedness, response

Clinical management of human infection with pandemic (H1N1) 2009: revised guidance

Publication details

Publication date: November 2009


This guidance provides updated information for health care providers managing patients with suspected or confirmed pandemic (H1N1) 2009. It incorporates knowledge gained about clinical features of pandemic influenza through international consultations.

Key topics:

  • risk factors for severe disease
  • signs and symptoms of progressive disease
  • diagnosis
  • treatment, both outpatient and in hospitals, and
  • clinical care for resource-poor settings.



Uncomplicated influenza can be diagnosed based on signs and symptoms presented by patients when influenza is known to be circulating in a community.

All patients should be advised to return to their health care provider for follow-up if they develop signs or symptoms of progressive disease.

Signs of progressive illness can include:

  • persistent high fever beyond 3 days
  • shortness of breath or difficulty in breathing, or turning blue
  • bloody or coloured sputum, chest pain or low blood pressure
  • in children, fast or laboured breathing
  • drowsiness, confusion or severe weakness
  • dehydration, which can cause dizziness, decreased urine output or lethargy.

Diagnostic testing to confirm the pandemic virus should be prioritized for patients at higher risk for severe illness.

However, clinicians who should not delay treatment of a patient with symptoms of an influenza-like illness to wait for laboratory confirmation of H1N1 virus infection.


Mild illness continues to characterize most cases, and basic supportive care (to relieve aches or fever) is sufficient for most people. However, health care providers should give all of their patients guidance on how to recognize signs of progressive illness, and when to seek medical attention.

For pregnant women, WHO advises early antiviral treatment for suspected or confirmed pandemic influenza illness.

Infants and very young children (those under 2 years of age), especially those with underlying conditions, should also be treated with antiviral medication if warning symptoms arise.

In general, antiviral treatment recommendations are:

  • Patients who have severe or progressive illness should be treated with antiviral medication as soon as possible.
  • People with mild symptoms but who are at higher risk for severe illness (e.g. pregnant women, infants and young children, and those with chronic lung problems) should start antiviral treatment as soon as possible.
  • Antiviral treatment is not necessary for people have uncomplicated, or mild, illness and are not in a high risk group for severe illness.

Mothers who are breastfeeding can continue breastfeeding while ill and receiving antiviral treatment.

In hospital settings, health providers should monitor oxygen levels closely and supplement oxygen as needed, following guidelines. When pneumonia is present patients should be treated with both antiviral medication and antibiotics as early as possible.

Advice for how to evaluate and care for severely ill patients in hospital settings is explained.

Resource-poor settings

In health care settings where resources are limited, clinical care should focus on early use of primary health care (by the family doctor or at health clinics, for example) to determine what type of care or treatment is necessary for a patient, and to set priorities for who needs hospital care most urgently. Health care decisions should be based on signs and symptoms of illness, and the level of influenza activity in the local area.

Decentralizing stocks of antiviral medications, even if supplies are limited, is important to reach at-risk groups and disadvantaged populations.

Related links