Dr. Alper is medical director of clinical reference products for EBSCO Publishing Inc., in Ipswich, Mass., and editor-in-chief of DynaMed (www.ebscohost.com/dynamed), a database that contains a more comprehensive and continually updated summary of this and more than 3,000 other clinical topics.
Note: This article was current when written on May 7, 2009 (posted on May 15, 2009) but information (including management guidelines) has changed daily. See www.ebscohost.com/dynamed for current information.
Description
- Major concern due to risk of “imminent pandemic”
- Newly identified influenza virus A/California/04/2009 A (H1N1) contains genetic components from human, swine and avian strains
- Human-to-human transmission by exposure to respiratory droplets or contaminated surfaces; not transmitted by eating pork
Also called
- Swine influenza; swine flu
- Swine-origin influenza virus (S-OIV)
- H1N1 influenza; H1N1 flu
- Novel H1N1 influenza
ICD-9 codes
- 487.0 influenza with pneumonia
- 487.1 influenza with other respiratory manifestations
- 487.8 influenza with other manifestations
CDC case definitions
- Influenza-like illness (ILI) -- fever plus sore throat or cough
- Confirmed case -- person with ILI with novel influenza A (H1N1) virus infection CDC laboratory confirmed by real-time reverse transcriptase polymerase chain reaction (RT-PCR) or viral culture
- Probable case -- person with ILI who is positive for influenza A, but negative for H1 and H3 by influenza RT-PCR
- Suspected case - person who
- does not meet confirmed or probable case definition
- is not novel H1N1 test negative
- has ILI in 1 of following situations
- previously healthy person < 65 years old hospitalized for ILI
- travel to state or country with ≥ 1 confirmed or probable cases
- epidemiologic link in past 7 days to confirmed or probable case
Symptoms
Differential diagnosis
- Influenza (non-avian, non-swine)
- Avian influenza
- Other viral flulike syndrome -- difficult to distinguish clinically
- Carbon monoxide poisoning
- Bacterial respiratory infection
Diagnostic testing
- Check local public health recommendations for patient selection for testing and use of rapid antigen tests.
- Interpretation and management of rapid test results vary by community and timing of outbreak.
- Respiratory swab generally needed in first four to five days of illness for viral detection, but some persons (especially children) may shed virus for > 10 days
- Send nasopharyngeal swab or nasal aspirate to appropriate public health laboratory for real-time PCR.
- Nasal swab or oropharyngeal swab are acceptable (but not preferred) for specimen collection
- Swab should have synthetic tip on plastic or aluminum shaft.
- Place in 1-3 mL of sterile viral transport media.
- Store in refrigerator until shipped on dry ice in appropriate packaging.
Prognosis (case numbers updated May 20, 2009)
- Among 10, 243 cases reported worldwide, 80 deaths have occurred (0.8% case fatality rate)
- Among 2,059 cases confirmed in Mexico, 56 deaths reported
- In United States
- Among 2,600 confirmed cases, mostly mild, but 3 deaths reported
- 35-36 patients have been hospitalized (different numbers reported)
- Many patients have had self-limited respiratory illness similar to typical seasonal influenza
- Deaths have been reported with prior cases of swine flu
- 7 deaths reported among 50 cases identified in literature review (search date 2006 Apr), including 1 soldier from outbreak in Fort Dix, New Jersey
- Case reports of fatal swine influenza
- 32-year-old pregnant woman hospitalized for pneumonia caused by swine influenza
- Immunocompetent women who developed adult respiratory distress syndrome caused by swine influenza
- Individuals at high risk for complications include
- Patients with chronic medical conditions or immunosuppression
- Patients ≤ 5 or ≥ 50 years old
- Children and adolescents taking chronic aspirin therapy (risk for Reye syndrome)
- Pregnant women
- Patients in chronic-care facilities
Treatment
- Recommendations may change as data on antiviral susceptibilities become available.
- Antiviral resistance testing for cases in US in April 2009 found 100% susceptibility to oseltamivir (Tamiflu) or zanamivir (Relenza) and 100% resistance to amantadine and rimantadine.
- Seasonal influenza virus antiviral sensitivities vary with subtype.
- Antiviral treatment for five days
- Oseltamivir 75 mg orally twice daily (lower dosing for children 0-13 years old)
- Zanamivir 10 mg (2 inhalations) via inhaler twice daily for patients >7 years old
- If possibility of H1N1 or seasonal influenza, use either zanamivir, or combination of oseltamivir plus amantadine or rimantadine.
- Supportive measures – antipyretics, oral fluids, nutrition, bed rest
- Avoid aspirin in children ≤ 18 years old due to risk of Reye syndrome.
- Preventive measures for patients, caregivers, close contacts, and health-care professionals
- Antiviral chemoprophylaxis for high-risk close contacts
- Social distancing, respiratory etiquette, face masks
Prevention
- No vaccine available
- General precautions
- Frequent handwashing
- Covering coughs and sneezes
- Advising ill persons to stay home (except to seek medical care) and minimize contact with others in household
- Voluntary home quarantine of household contacts
- Reduction of unnecessary social contacts
- Place patients with confirmed, probable or suspected case in single-patient room with door kept closed.
- Limit entry to isolation room to health-care providers performing direct patient care.
- Gown, gloves, eye protection and N95 respirator for persons providing care
- Ill patient should wear surgical mask when outside of patient room and wash hands frequently.
- Antiviral chemoprophylaxis
- Oseltamivir or zanamivir once daily during exposure period and for 10 days after last known exposure
- Indicated for
- Close contacts (of confirmed, probable, or suspected case) at high risk for complications of influenza
- Chronic medical conditions
- Aged ≥65 years
- Aged ≤5 years
- Pregnant women
- Health-care workers, public health workers or first responders who have recognized unprotected close contact during a case's infectious period
For complete references, see www.ebscohost.com/dynamed.