FLU BABI / H1N1/ Swine Influenza

Interim Guidance for Clinicians on Identifying and Caring for Patients with Swine-origin Influenza A (H1N1) Virus Infection


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.
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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 at http://www.journals.uchicago.edu/doi/pdf/10.1086/511159?cookieSet=1 .
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

H1N1 Flu (Swine Flu)
Site last updated May 13, 2009, 11:00 AM ET
U.S. Human Cases of H1N1 Flu Infection
(As of May 13, 2009, 11:00 AM ET)

States* Laboratory confirmed cases Deaths
45 states* 3352 cases 3 deaths
*includes the District of Columbia
This table will be updated daily Monday-Friday at around 11 AM ET.
International Human Cases of Swine Flu Infection, see World Health Organization.

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See Also:
FluView Surveillance Report (277 KB)
For the week ending May 2, 2009

A New Virus Emerges
Novel influenza A (H1N1) is a new flu virus of swine origin that was first detected in April, 2009. The virus is infecting people and is spreading from person-to-person, and has sparked a growing outbreak of illness in the United States with an increasing number of cases being reported internationally as well.
CDC anticipates that there will be more cases, more hospitalizations and more deaths associated with this new virus in the coming days and weeks because the population has little to no immunity against it. Novel influenza A (H1N1) activity is now being detected in two of CDC’s routine influenza surveillance systems as reported in the May 8, 2009 FluView. FluView is a weekly report that tracks U.S. influenza activity through multiple systems across five categories.
The May 8 FluView found that the number of people visiting their doctors with influenza-like-illness is higher than expected in the United States for this time of year. Second, laboratory data shows that regular seasonal influenza A (H1N1), (H3N2) and influenza B viruses are still circulating in the United States, but novel influenza A (H1N1) and “unsubtypable”* viruses now account for a significant number of the viruses detected in the United States.
It’s thought that novel influenza A (H1N1) flu spreads in the same way that regular seasonal influenza viruses spread; mainly through the coughs and sneezes of people who are sick with the virus.
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.
Increased 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. This increase in testing will likely result in an increase in the number of confirmed cases of illness reported. This, combined with ongoing monitoring through Flu View should provide a fuller picture of the burden of disease in the United States over time.
CDC is issuing updated interim guidance daily in response to the rapidly evolving situation.
Clinician Guidance
CDC has issued interim guidance for clinicians on identifying and caring for patients with novel H1N1, in addition to providing interim guidance on the use of antiviral drugs. Influenza antiviral drugs are prescription medicines (pills, liquid or an inhaler) with activity against influenza viruses, including novel influenza H1N1 viruses. The priority use for influenza antiviral drugs during this outbreak is to treat severe influenza illness, including people who are hospitalized or sick people who are considered at high risk of serious influenza-related complications.
Public Guidance
In addition, 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. Novel H1N1 infection has been reported to cause a wide range of symptoms, including fever, cough, sore throat, body aches, headache, chills and fatigue. In addition, a significant number of people also have reported nausea, vomiting or diarrhea. 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.
*Unsubtypable viruses are viruses that through normal testing cannot be subtyped as regularly occurring human seasonal influenza viruses. In the context of the current outbreak, it’s likely that most of these unsubtypable viruses are novel H1N1.