Introduction

The audiences for this guidance document are the National Focal Points for the International Health Regulations (IHR(2005)) and competent national public health authorities. The primary focus of this guidance document is global surveillance. It also gives some suggestions on the types of signals that Member States and IHR States Parties can capture in their event‐based surveillance. These signals can aid identification of individuals for whom investigation of swine influenza A(H1N1) virus infection is warranted.

This is an interim WHO guidance on the global surveillance of the emerging swine influenza A(H1N1) virus infection. This is a living document that will be reviewed on a weekly basis and modified in accordance with changes in the epidemiology of this virus. As the event evolves, there will be a need to switch surveillance activities to the longer‐term monitoring of the disease. WHO will alert countries when a change in surveillance objectives and methods occurs. WHO’s data requirements will remain as flexible as possible to accommodate different surveillance systems and reporting capacity around the world.

This document will form part of a suite of guidance documents being produced by WHO in response to this public health emergency of international concern as determined by the Director General of WHO on 25 April 2009. New influenza virus sub‐types and clusters of unknown and unusual disease are notifiable to WHO in accordance with the Annex 2 decision instrument of the IHR (2005).

At this early stage of the outbreak of swine influenza A(H1N1) virus, the main aims of surveillance are the early warning of virus spread and laboratory confirmation of virus circulating in new geographical areas and countries. Accordingly, WHO encourages all Member States and IHR States Parties to enhance their surveillance and diagnostic capacity for influenza and other acute respiratory infections, building on exiting surveillance structure and resources.

Objectives of enhanced global surveillance for human infections with swine influenza A(H1N1) virus

Specific objectives of this surveillance activity are to guide global prevention and control activities through the following actions: 1. Detect and confirm cases of swine influenza A(H1N1) virus infection 2. Establish the extent of international spread of swine influenza A(H1N1) virus infection 3. Assist in the early severity assessment of the disease

Case definitions for infections with swine influenza A(H1N1) Virus In order to understand the spectrum of severity of the disease caused by swine influenza A(H1N1) virus infection , the clinical case description includes both mild form of influenza‐like illness (ILI) and more severe forms (lower respiratory tract infections including pneumonia and severe acute respiratory illness (SARI)). In addition, asymptomatic laboratory‐confirmed infections should be reported.

The following case definitions are for the purpose of reporting probable and confirmed cases of swine influenza A(H1N1) virus infection to WHO.