H1N1

Novel H1N1 Flu: CDC Response
CDC continues to take aggressive action to respond to the outbreak. CDC’s response goals are to reduce the spread and severity of illness, and to provide information to help health care providers, public health officials and the public address the challenges posed by this new public health threat.
CDC is issuing updated interim guidance in response to the rapidly evolving situation.
Clinician Guidance
CDC has issued interim guidance for clinicians on identifying and caring for patientswith novel H1N1, in addition to providing interim guidance on the use of antiviral drugs. Influenza antiviral drugs are prescription medicines (pills, liquid or an inhaled powder) with activity against influenza viruses, including novel influenza H1N1 viruses. The priority use for influenza antiviral drugs during this outbreak is to treat people hospitalized with influenza illness, and to treat people at increased risk of severe illness, including pregnant women, young children, and people with chronic health conditions like asthma, diabetes and other metabolic diseases, heart or lung disease, kidney disease, weakened immune systems, and persons with neurologic or neuromuscular disease.
Public Guidance
CDC has provided guidance for the public on what to do if they become sick with flu-like symptoms, including infection with novel H1N1. CDC also has issued instructions on taking care of a sick person at home and the use of facemasks and respirators to reduce novel influenza A (H1n1) transmission. Everyone should take everyday preventive actions to stop the spread of germs, including frequent hand washing and people who are sick should stay home and avoid contact with others in order to limit further spread of the disease.
Testing
CDC has developed a PCR diagnostic test kit to detect this novel H1N1 virus and has now distributed test kits to all states in the U.S. and the District of Columbia and Puerto Rico. The test kits are being shipped internationally as well. This will allow states and other countries to test for this new virus.
Vaccine
Vaccines are a very important part of a response to novel H1N1 influenza and the U.S. Government is aggressively taking early steps in the process to manufacture a novel H1N1 vaccine, working closely with manufacturers. CDC isolated the new H1N1 virus, made a candidate vaccine virus strain that can be used to create vaccine, and is working with other agencies and industry to begin scaling up for testing and production of a vaccine. Making vaccine is a long multi-step process requiring several months to complete. CDC has developed guidance for state and local public health departments to assist them in planning for a novel H1N1 influenza vaccination campaign. Additional guidance is forthcoming.
Stockpile Deployment
CDC has deployed 25 percent of the supplies in the Strategic National Stockpile (SNS) to all states in the continental United States and U.S. territories. This included antiviral drugs, personal protective equipment, and respiratory protection devices. These supplies and medicines will help states and U.S. territories respond to novel H1N1 virus.
Surveillance
Novel influenza A (H1N1) activity is being detected through CDC’s routine influenza surveillance systems and reported weekly in FluView. CDC tracks U.S. influenza activity through multiple systems. While our influenza surveillance systems indicate that overall influenza activity is decreasing in the United States, novel H1N1 outbreaks are ongoing in different parts of the U.S., in some cases with intense influenza-like activity. Nearly 100 percent of the influenza viruses being detected now are novel H1N1 viruses.
School Dismissal Monitoring
CDC and the U.S. Department of Education, in collaboration with state and local health and education agencies and national non-governmental organizations, have implemented a school dismissal monitoring system for the 2009-2010 school year. This monitoring system will generate real-time, national summary data daily on the number of school dismissals and the number of impacted students and teachers. To report a school dismissal click here.
Interim Guidance for Clinicians on Identifying and Caring for Patients with Swine-origin Influenza A (H1N1) Virus Infection
May 4, 2009 4:45 PM ET
On this Page
· Transmission
· Incubation period
· Persons with confirmed novel influenza A (H1N1) virus infection
· Clinical findings
· Complications
· Groups at high risk for complications
· Medical care for patients with novel influenza A (H1N1) virus
· Which patients should be tested for novel influenza A (H1N1) virus
· Reporting suspect novel influenza A (H1N1) virus infection
· Treatment of novel influenza A (H1N1)
· Additional Therapy
· Infectious period
· Infection Control measures
· Antiviral chemoprophyaxis
· Additional Information
Objective: This document provides interim guidance for clinicians who might provide care for patients with confirmed novel influenza A (H1N1) or suspected novel influenza A (H1N1) virus infection (previously referred to as swine-origin influenza virus). This document has changed as more ill persons have been identified and more epidemiologic and clinical information has been gathered. CDC recommends that testing be prioritized for those with severe respiratory illness and those at highest risk of complications from influenza, as reflected in this document.
Transmission
Transmission of novel influenza A (H1N1) is being studied as part of the ongoing outbreak investigation, but limited data available indicate that this virus is transmitted in ways similar to other influenza viruses. Seasonal human influenza viruses are thought to spread from person to person primarily through large-particle respiratory droplet transmission (e.g., when an infected person coughs or sneezes near a susceptible person). Transmission via large-particle droplets requires close contact between source and recipient persons because droplets do not remain suspended in the air and generally travel only a short distance (< 6 feet). Contact with contaminated surfaces is another possible source of transmission and transmission via droplet nuclei (also called “airborne” transmission). Because data on the transmission of novel H1N1 viruses are limited, the potential for ocular, conjunctival, or gastrointestinal infection is unknown. Since this is a novel influenza A virus in humans, transmission from infected persons to close contacts might be common. All respiratory secretions and bodily fluids (diarrheal stool) of novel influenza A (H1N1) cases should be considered potentially infectious.
Incubation period
The estimated incubation period is unknown and could range from 1-7 days, and more likely 1-4 days.
Persons with confirmed novel influenza A (H1N1) virus infection
View the Case definitions for Confirmed, Probable and Suspected cases.
Clinical findings
Patients with uncomplicated disease due to confirmed novel influenza A (H1N1) virus infection have experienced fever, chills, headache, upper respiratory tract symptoms (cough, sore throat, rhinorrhea, shortness of breath), myalgias, arthralgias, fatigue, vomiting, or diarrhea. In New York City, 95% of patients with novel influenza A (H1N1) met the case definition for influenza-like illness (subjective fever plus cough and/or sore throat) (Swine-Origin Influenza A (H1N1) Virus Infections in a School --- New York City, April 2009)
Complications
There is insufficient information to date about clinical complications of this novel influenza A (H1N1) virus infection. Among persons infected with previous variants of swine influenza viruses, clinical syndromes have ranged from mild respiratory illness, to lower respiratory tract illness, dehydration, or pneumonia. Deaths caused by previous variants of swine influenza viruses have occasionally occurred. Although data on the spectrum of illness is not yet available for this novel influenza A (H1N1), clinicians should expect complications to be similar to seasonal influenza: exacerbation of underlying chronic medical conditions, upper respiratory tract disease (sinusitis, otitis media, croup) lower respiratory tract disease (pneumonia, bronchiolitis, status asthmaticus), cardiac (myocarditis, pericarditis), musculoskeletal (myositis, rhabdomyolysis), neurologic (acute and post-infectious encephalopathy, encephalitis, febrile seizures, status epilepticus), toxic shock syndrome, and secondary bacterial pneumonia with or without sepsis.
Groups at high risk for complications
Currently, insufficient data are available to determine who is at higher risk for complications of novel influenza A (H1N1) virus infection. Thus, at this time, the same age and risk groups who are at higher risk for seasonal influenza complications should also be considered at higher risk for swine-origin influenza complications.
Groups at higher risk for seasonal influenza complications include:
· Children less than 5 years old;
· Persons aged 65 years or older;
· Children and adolescents (less than 18 years) who are receiving long-term aspirin therapy and who might be at risk for experiencing Reye syndrome after influenza virus infection;
· Pregnant women;
· Adults and children who have chronic pulmonary, cardiovascular, hepatic, hematological, neurologic, neuromuscular, or metabolic disorders;
· Adults and children who have immunosuppression (including immunosuppression caused by medications or by HIV);
· Residents of nursing homes and other chronic-care facilities.
Medical care for patients with novel influenza A (H1N1) virus
Not all patients with suspected novel influenza (H1N1) infection need to be seen by a health care provider. Patients with severe illness and those at high risk for complications from influenza (see list above) should contact their medical provider or seek medical care.
Which patients should be tested for novel influenza A (H1N1) virus
Clinicians should test persons for the novel influenza (H1N1) virus if they have an acute febrile respiratory illness or sepsis-like syndrome. Certain groups may have atypical presentations including infants, elderly and persons with compromised immune systems. Priority for testing includes persons who 1) require hospitalization or 2) are at high-risk for severe disease (as listed above). To test for novel H1N1 influenza virus, upper respiratory specimens, such as a nasopharyngeal swab or aspirate, nasal swab plus a throat swab or nasal wash, or tracheal aspirate should be collected. Persons who perform nasal and tracheal aspirate collections on ill persons require appropriate personal protective equipment. Specimens should be sent to the state public health laboratory. Not all people with suspected novel influenza (H1N1) infection need to have the diagnosis confirmed, especially if the person resides in an affected area or if the illness is mild. Recommendations on who to test may differ by state or community. Clinicians should be aware of local guidance on testing and should use their clinical judgment in addition to this guidance for deciding when to test for novel influenza A (H1N1). View the Interim guidance on specimen collection, processing, and testing.
Reporting suspect novel influenza A (H1N1) virus infection
Clinicians should contact their state public health department if they test a person for novel influenza A (H1N1) infection to obtain information on what clinical and epidemiological data to collect and specimen shipment protocols in their state. See also Information on laboratory testing and specimen collection.
Treatment of novel influenza A (H1N1)
The novel influenza (H1N1) virus is susceptible to both oseltamivir and zanamivir. It is resistant to amantadine and rimantadine. View Interim guidance on antiviral treatment for novel influenza A (H1N1).
Additional Therapy
Additional therapy such as antibacterial agents, should be used at the discretion of the clinicians given the patients clinical presentation. For antibacterial treatment of pneumonia, clinical guidance for community-acquired pneumonia should be followed and can be accessed here.
For hospitalized patients with severe community-acquired pneumonia (CAP) requiring intensive care unit admission, menthicillin-resistent Staphylococcus aureus (MRSA) infection should be suspected and treated empirically in addition to other causes of CAP if they have 1) necrotizing or cavitary infiltrates or 2) empyema.
Infectious period
The duration of shedding with novel influenza A (h1N1) virus is unknown. Therefore, until data are available, the estimated duration of viral shedding is based upon seasonal influenza virus infection.. Infected persons are assumed to be shedding virus from one day prior to illness onset until resolution of symptoms. In general, persons with novel influenza A (H1N1) virus infection should be considered potentially infectious from one day before to 7 days following illness onset. Children, especially younger children, might be infectious for up to 10 days.
Infection control measures

View the guidance on infection control during care of patients with confirmed or suspected novel influenza A (H1N1) virus infection.
Antiviral chemoprophylaxis
View the guidance on pre-exposure and post-exposure chemoprophylaxis with antiviral agents for novel influenza A (H1N1) virus can be found at
Novel H1N1 Flu: International Situation Update
August 7, 2009, 11:00 AM ET
Map of International Activity Estimates(Including Novel H1N1)
This situation report provides an update to the international situation as of August 4, 2009. World Health Organization (WHO) regions have reported 162,380 laboratory-confirmed cases of novel influenza A (H1N1) and 1,154 deaths. The laboratory-confirmed cases represent an underestimation of total cases in the world as many countries have shifted to strategies of clinical confirmation and prioritization of laboratory testing for only persons with severe illness and/or high risk conditions. The novel influenza A (H1N1) virus is the dominant influenza virus in circulation in the United States, England, South Africa, New Zealand, Australia, Chile, Argentina and Brazil. South Africa has had a notable increase in the proportion of influenza that is novel influenza A (H1N1), and now it represents the majority of influenza in the country. Many seasonal influenza viruses from these countries have not been subtyped. Of those that have been subtyped in Australia, South Africa, and Argentina, the most common seasonal influenza virus is influenza A (H3N2).
Selected Highlights
· Novel influenza A (H1N1) continues to circulate widely.
· Descriptive epidemiology of cases remains similar across countries.
· Isolates sequenced at WHO and CDC suggest that circulating novel influenza A (H1N1) viruses look similar to A/California/07/2009 (the reference virus selected by WHO as a potential candidate for novel influenza A (H1N1) vaccine).
International Resources for Novel H1N1 Information
Health Organizations
· World Health Organization (WHO)
· ECDC (European Centre for Disease Prevention and Control)
· H2P (Humanitarian Pandemic Preparedness)
· Public Health Agency of Canada
World Health Organization (WHO) Regional Offices
· AFRO (WHO Regional Office for Africa)
· AMRO (WHO Regional Office for the Americas) / PAHO (Pan American Health Organization)
· EMRO (WHO Regional Office for the Eastern Mediterranean)
· EURO (WHO Regional Office for Europe)
· SEARO (WHO Regional Office for South-East Asia)
· WPRO (WHO Regional Office for the Western Pacific)
Travel and Novel H1N1 Flu
Human cases of novel H1N1 flu virus infection have been identified in the United States and several countries around the world. For information on novel H1N1 flu and travel, see the CDC H1N1 Flu and Travel website.
Reports and Publications
· ECDC Interim Risk Assessment Influenza A (H1N1) 2009 PandemicIssued July 30, 2009 - This document provides an interim risk assessment of novel H1N1 flu in Europe prepared by ECDC.
· World Health Organization Weekly Epidemiological record – Issued July 24, 2009 This document by WHO provides updates on the international novel H1N1 flu situation.
· MMWR – Update: Novel Influenza A (H1N1) Virus Infection – Mexico, March-May, 2009 – Issued June 5, 2009 / Vol. 58 / No. 21.This Morbidity and Mortality Weekly Report describes the novel influenza A (H1N1) outbreak in Mexico from March-May, 2009.
· MMWR – Update: Novel Influenza A (H1N1) Virus Infections – Worldwide, May 6, 2009 – Issued May 8, 2009 / Vol. 58 / No. 17.This Morbidity and Mortality Weekly Report describes worldwide novel influenza A (H1N1) infections as of May 6, 2009.
· Links to non-federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the federal government, and none should be inferred. CDC is not responsible for the content of the individual organization Web pages found at these links.