WHO: Clinical management of human infection with pandemic influenza (H1N1) 2009: Revised guidance

November 2009
Introduction
A novel influenza A (H1N1) virus of swine origin emerged among people in Mexico
during the spring of 2009 and spread with travellers worldwide, resulting in the first
influenza pandemic since 1968. As of October 2009, 195 countries have reported
confirmed human cases of pandemic (H1N1) 2009. While the majority of illnesses caused by pandemic (H1N1) 2009 virus infection have been self-limited mild-to-moderate uncomplicated disease, severe complications including fatal outcomes have been reported.

The pandemic (H1N1) 2009 influenza virus differs in its pathogenicity from seasonal
influenza in two key aspects. First, as the majority of human population has little or no pre-existing immunity to the virus, the impact of the infection has been in a wider age range, in particular among children and young adults. Secondly, the virus can infect the lower respiratory tract and cause rapidly progressive pneumonia especially in children and young to middle-aged adults.

In October 2009, WHO convened an international consultation represented by all WHO Regions, in Washington, DC, USA, to revise the guidance on clinical management of patients with pandemic (H1N1) 2009 virus infection. Experts in public health, laboratory science, pathology, and clinical care came together to review the published evidence to date and to share unpublished data. This document incorporates the knowledge made available to WHO and updates previous WHO guidance. Additional WHO guidance on pharmacological management, as well as infection control recommendations for health care facilities, are available separately. We anticipate commissioning full evidence reviews in preparation for another international consultation in 2010. This clinical guidance will then be revised accordingly, based upon new information. The purpose of this document is to provide information for clinicians managing patients with suspected or confirmed pandemic (H1N1) 2009 virus infection.
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Signs and symptoms of progressive disease
Patients who present initially with uncomplicated influenza may progress to more severe disease. Progression can be rapid (i.e. within 24 hours). The following are some of the indicators of progression, which would necessitate an urgent review of patient management:
• Symptoms and signs suggesting oxygen impairment or cardiopulmonary insufficiency:
- Shortness of breath (with activity or at rest), difficulty in breathing2, turning
blue, bloody or coloured sputum, chest pain, and low blood pressure;
- In children, fast or laboured breathing; and
- Hypoxia, as indicated by pulse oximetry.
• Symptoms and signs suggesting CNS complications:
- Altered mental status, unconsciousness, drowsiness, or difficult to awaken and
recurring or persistent convulsions (seizures), confusion, severe weakness, or
paralysis.
• Evidence of sustained virus replication or invasive secondary bacterial infection
based on laboratory testing or clinical signs (e.g. persistent high fever and other
symptoms beyond 3 days).
• Severe dehydration, manifested as decreased activity, dizziness, decreased urine
output, and lethargy.

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