April 29, 2009 2:00 AM ET
Objective: This document provides interim guidance for clinicians who might provide care for patients with swine-origin influenza A (H1N1) or suspected swine-origin influenza A (H1N1) virus infection. It will be periodically updated as information becomes available.
Transmission of swine-origin 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 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 (<1 meter) through the air. Contact with respiratory-droplet contaminated surfaces is another possible source of transmission. Because data from swine-origin influenza 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 swine-origin influenza A (H1N1) cases should be considered potentially infectious.
The estimated incubation period is unknown and could range from 1-7 days, and more likely 1-4 days.
Persons with confirmed Swine-origin influenza A (H1N1) virus infection
A confirmed case of S-OIV infection is defined as a person with an acute febrile respiratory illness with laboratory confirmed S-OIV infection at CDC by one or more of the following tests:
- real-time RT-PCR
- viral culture
Case definitions for Probable and Suspected cases can be found at: http://www.cdc.gov/swineflu/casedef_swineflu.htm
Clinicians should suspect swine-origin influenza A (H1N1) in persons with an acute febrile respiratory illness who
- Have had close contact with a person who is a swine-origin influenza confirmed case or
- Traveled to a community in the United States or internationally where there are one or more confirmed swine-origin influenza cases (Updated information about areas with confirmed human cases of swine-origin influenza A (H1N1) can be found at http://www.cdc.gov/swineflu/investigation.htm.) or
- Reside in a community where there are one or more confirmed swine-origin influenza A (H1N1) cases.
Patients with uncomplicated disease due to confirmed swine-origin influenza A (H1N1) virus infection have experienced fever, headache, upper respiratory tract symptoms (cough, sore throat, rhinorrhea), myalgia, fatigue, vomiting, or diarrhea.
There is insufficient information to date about clinical complications of this variant of swine-origin influenza A (H1N1) virus infection. Among persons infected with previous variants of swine influenza virus, clinical syndromes have ranged from mild respiratory illness, to lower respiratory tract illness, dehydration, or pneumonia. Deaths caused by previous variants of swine influenza have occasionally occurred. Although data on the spectrum of illness is not yet available for this new variant of swine-origin 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
There are insufficient data available at this point to determine who is at higher risk for complications of swine-origin influenza A (H1N1) virus infection. At this time, the same age and risk groups who are at higher risk for seasonal influenza complications should also beconsidered at higher risk for swine-origin influenza complications .
High risk groups for seasonal influenza complications include: infants aged 12–24 months; HIV-infected persons; adults aged >65 years, residents of any age of nursing homes or other long-term care institutions; and persons with asthma or other chronic pulmonary diseases, such as cystic fibrosis in children or chronic obstructive pulmonary disease in adults, hemodynamically significant cardiac disease ,immunosuppressive disorders or who are receiving immunosuppressive drugs, sickle cell anemia and other hemoglobinopathies, diseases that requiring long-term aspirin therapy, such as rheumatoid arthritis or Kawasaki disease, chronic renal dysfunction, cancer, chronic metabolic disease, such as diabetes mellitus, neuromuscular disorders, seizure disorders, or cognitive dysfunction that may compromise the handling of respiratory secretions.
Reporting suspect swine-origin influenza A (H1N1) virus infection
Clinicians should contact their state public health department to report suspected cases of swine-origin influenza A (H1N1) virus infection and to obtain information on what clinical and epidemiological data to collect and specimen shipment protocols in their state.
Testing for swine-origin influenza A (H1N1) virus
Clinicians should consider testing suspected cases of swine-origin influenza A (H1N1), especially those with severe illness, by obtaining an upper respiratory specimens, such as a nasopharyngeal swab or wash, or nasal wash/aspirate, or tracheal aspirate, to test for swine-origin influenza A (H1N1) virus. Specimens should be tested by the state public health laboratory. Interim guidance on specimen collection ,processing, and testing for patients with suspected swine-origin influenza A (H1N1) virus infection can be found at: http://www.cdc.gov/swineflu/specimencollection.htm
Treatment for swine-origin influenza A (H1N1)
The swine-origin influenza virus is susceptible to both oseltamivir and zanamivir. It is resistant to amantadine and rimantadine. Interim guidance on antiviral treatment for swine-origin influenza A (H1N1) can be found at: http://www.cdc.gov/swineflu/recommendations.htm
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.
The duration of shedding with swine-origin 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 the day prior to illness onset until resolution of symptoms. Persons with swine-origin influenza A (H1N1) virus infection should be considered potentially contagious for up to 7 days following illness onset. Persons who continue to be ill longer than 7 days after illness onset should be considered potentially contagious until symptoms have resolved. Children, especially younger children, might be contagious for longer periods.
Infection Control Measures
Guidance on infection control during care of patients with confirmed or suspected swine-origin influenza A (H1N1) virus infection can be found at: http://www.cdc.gov/swineflu/guidelines_infection_control.htm
Guidance on pre-exposure and post-exposure chemoprophylaxis with antiviral agents for swine-origin influenza A (H1N1) virus can be found at: http://www.cdc.gov/swineflu/recommendations.htm
Additional information on swine-origin influenza can be found at: http://www.cdc.gov/swineflu/