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Interim CDC Guidance for Nonpharmaceutical Community Mitigation in Response to Human Infections With Swine Influenza (H1N1) Virus

April 28, 2009

These recommendations are based on current information and are subject to change based on ongoing surveillance and continuous risk assessment.


This document provides interim planning guidance for state, territorial, tribal, and local communities that focuses on several nonpharmaceutical measures that might be useful during this outbreak of swine influenza A (H1N1) virus aimed at reducing disease transmission and associated morbidity and mortality.

Human cases of swine influenza A (H1N1) virus infection have been identified in several states and in other countries. This is a novel influenza A virus that has not been identified in people before, and human-to-human transmission of the virus appears to be ongoing. Unlike the experience in Mexico, the United States is currently observing a less severe clinical spectrum of disease with infection by the identical virus strain. As of April 26, 2009, of the confirmed cases of swine influenza A (H1N1) virus infection, only two confirmed case-patients were hospitalized and none have died in the United States. Mexican health officials have reported several hundred suspect cases, including several deaths associated with confirmed swine influenza A (H1N1) virus infection. In Mexico, many patients have experienced rapidly progressive pneumonia, respiratory failure requiring mechanical ventilation and acute respiratory distress syndrome (ARDS). Therefore, the experience of these two countries has been markedly different to date. Getting better information to explain these differences is a high priority for the ongoing investigation.

The previously published United States government guidance on community mitigation relies on knowledge of the Pandemic Severity Index (PSI) to characterize the severity of a pandemic and identify the recommendations for specific interventions that communities may use for a given level of severity, and suggests when these measures should be started and how long they should be used.

The substantial difference in the severity of the illness associated with infections from the same virus, the relatively low number of cases detected in the United States, and insufficient epidemiologic and clinical data to ascribe a PSI, present a formidable challenge in terms of assessing the threat posed by this novel influenza A virus until additional epidemiologic and virologic information is learned.

Novel influenza A virus infections in humans, including swine influenza A (H1N1) virus, represent a pandemic threat. Recognizing the historical precedent for the emergence of a pandemic influenza virus which could have waves of disease with different morbidity and mortality and epidemiologic profiles, public health departments in the United States must remain vigilant.

It is prudent for communities to act in the absence of sufficient data to protect their citizens and take advantage of a narrow window of opportunity for intervention. CDC recommends that affected states with at least one laboratory-confirmed case of swine influenza A (H1N1) virus infection consider activating community mitigation interventions for affected communities. As public health officials in the United States learn more about this emerging virus, updated guidance will be issued in conjunction with our state, local, tribal and territorial partners.


When Human Infection with Swine Influenza A (H1N1) Virus is Confirmed in a Community

Strongly Recommend Home Isolation of Cases:

Regarding Household Contacts:

School Dismissal and Childcare Facility*Closure:

Other Social Distancing Interventions:

These recommendations are subject to change as additional epidemiological and clinical data become available.

*Childcare facility: centers and facilities that provide care to any number of children in a nonresidential setting, large family childcare homes that provide care for seven or more children in the home of the provider and small family childcare homes that provide care to six or fewer children in the home of the provider.

Additional information can be found at the following Web sites:

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