References:
- Global Infectious Diseases and Epidemiology Online Network: Infectious Diseases of the Philippines, 2013 eBook Edition, ISBN 978-1-61755-582-4, by Stephen Berger. Accessed here.
| Agent | VIRUS - RNA. Orthomyxoviridae, Orthomyxovirus: Influenza virus |
| Reservoir | Human Occasionally Ferret Bird Pig |
| Vector | None |
| Vehicle | Droplet |
| Incubation Period | 1 to 3 days |
| Diagnostic Tests | Viral culture (respiratory secretions). Serology. Nucleic acid amplification techniques are available. |
| Typical Adult Therapy | Respiratory precautions. Influenza A or B: Oseltamivir 75 mg PO BID X 5d OR Zanamavir 10 mg BID X 5 days |
| Typical Pediatric Therapy | Respiratory precautions. Influenza A or B: Oseltamivir 2 mg/kg (max 75 mg) PO BID X 5d OR Zanamavir (age > 5 years) 10 mg BID X 5 days |
| Vaccine | Influenza - inactivated Influenza - live |
| Clinical Hints | Myalgia, headache, cough, fever; pharyngitis and conjunctivitis often present; usually encountered in the setting of an outbreak; leucocytosis, chest pain and lobar infiltrate herald bacterial (pneumococcal or staphylococcal) pneumonia. |
| Synonyms | Asian flu, Aviaire influenza, Avian flu, Avian influenza, Bird flu, Epidemic catarrh, Grippe, H1N1, H2N2, H3N2, H5N1, Hong Kong flu, LPAI, Spanish influenza, Swine flu, Swine influenza. |
Influenza is characterized by acute onset of fever, headache, myalgia, nonproductive cough, sore throat, and rhinitis.
- The illness usually resolves in 2 to 7 days; however, symptoms often persist for up to two weeks.
- Severe illness or death may complicate the acute infection, notably in pregnant women, the elderly and patients with underlying medical conditions.
- Complications include primary viral pneumonia or bacterial pneumonia (most commonly pneumococcal) 4 ; myocarditis, myositis, Guillain-Barre syndrome 5 , encephalitis 6 , Gianotti-Crosti syndrome and transverse myelitis.
WHO Case Definition for Surveillance: Influenza
A person with sudden onset of fever of >38°C and cough or sore throat in the absence of other diagnoses.
Laboratory criteria for diagnosis
- Virus isolation: Swab or aspirate from the suspected individual, or
- Direct detection of influenza viral antigen.
- Serology: Fourfold rise in antibody titer between early and late serum.
Case classification
- Suspected: A case that meets the clinical case definition.
- Confirmed: A case that meets the clinical case definition and is laboratory-confirmed (used mainly in epidemiological investigation rather than surveillance).
WHO Definition for Surveillance: Swine influenza (H1N1)
- Confirmed case: a person with swine influenza A (H1N1) virus infection laboratory confirmed by:
- Real-time RT-PCR and/or
- Viral culture and/or
- 4-fold rise in swine influenza A (H1N1) virus specific neutralizing antibodies
- Probably case: either a:
- person with influenza test positive for influenza A, but unsubtypable by reagents used to detect seasonal influenza virus infection, or
- person with clinically compatible illness or who died of unexplained acute respiratory illness who is considered to be epidemiologically linked to probable or confirmed case
CDC Definition for Surveillance: Swine influenza (H1N1)
- Confirmed case: a person with acute respiratory illness with swine influenza A (H1N1) virus infection laboratory confirmed at CDC by:
- Real-time reverse transcriptase polymerase chain reaction (RT-PCR) and/or
- Viral culture
- Probable case: a person with acute febrile respiratory illness who is:
- Positive for influenza A, but negative for H1 and H3 by influenza RT-PCR
- Positive for influenza A by influenza rapid test or influenza immunofluorescence assay (IFA) plus meets criteria for suspected case
- Suspected case: a person with acute respiratory illness (defined as recent onset of >= 2 of rhinorrhea or nasal congestion, sore throat, or cough) plus:
- Close contact to confirmed case of swine influenza A (H1N1) virus infection during case’s infectious period, or
- Close contact defined as within about 6 feet of ill person
- Infectious period defined as 1 day prior to illness onset to 7 days after onset
- Travel to or residence in area with confirmed cases of swine influenza A (H1N1) virus infection
Avian Influenza H5N1 Infection
Avian influenza H5N1 infection is characterized by fever greater than 38°C, shortness of breath and cough.
- The incubation period is 2 to 4 days.
- All patients reported to date have presented with significant lymphopenia and marked chest radiograph abnormalities consisting of diffuse, multifocal or patchy infiltrates.
- Some cases showed segmental or lobular consolidation with air bronchograms.
- Crackles were frequently heard on auscultation.
- Some of the patients reported sore throat, conjunctivitis, myalgia, rash or rhinorrhea.
- Watery diarrhea or loose stools was noted in approximately 50% of the cases.
- Myocardial dysfunction and hepatic dysfunction are also reported.
- Reactive hemophagocytic syndrome is the most characteristic pathological finding and may contribute to the lymphopenia, liver dysfunction, and abnormal clotting profiles observed among patients with severe infection.
- Approximately 90% of patients with H5N1 infection have been below age 40.
- Approximately 60% of patients have died, on an average of 10 days after onset of symptoms.