Swine Flu
- virulence
- transmission
- signs, symptoms, and diagnosis
- personal protection
- treatments
- consequences and course
- evoutionary pathway
- resources and references
Transmissable swine flu, as originated early 2009 in Mexico, is an H1N1 influenza A virus. It developed the capacity to spread from person-to-person, and has reached WHO phase 4 - or person-to-person spread - in at least two countries.
This virus is triply resorted, with DNA fragments from humans and pigs from both North America and Eurasia. It is a distinct strain, meaning existing vaccines are likely less helpful. It appears to accordingly be the result of significant antigenic drift, not shift.
People at increased risk of serious disease include:
- people 65 years of age or older
- residents of a long term care facility
- children 12-23 months
- people under 18 years of age on chronic acetylsalicylic acid therapy
- children and adults with serious chronic conditions (respiratory, cardiac, immunosuppression, renal, malignancy, diabetes, neuromuscular, seizure, cognitive dysfunction, others)
Virulence
1-4 days, average of 2 days, as long as 7 days.
Transmission
Influenza is spread mainly through droplets, or person-to-person spread. Coughing and sneezing are frequent sources of infectious droplets, though fomites may also play a role in infection.
Current data for swine flu are modelled after seasonal influenza dynamics, which state people are infectious from the day prior to illness onset until fever resolves, or up to 7 days post-onset. People at increased risk may be contagious for longer.
To reduce transmission, isolate people suspected of carrying the disease, avoid crowding (>1m between people), and ensure use of hand hygiene.
Signs, Symptoms, and Diagnosis
- history
- physical exam
- lab investigations
- diagnostic imaging
- differential diagnosis
History
For many people, swine flu causes uncomplicated disease. Symptoms include:
- fever
- myalgia
- fatigue
- lack of appetite
- headache
- upper respiratory tract symptoms (cough, sore throat, rhinorrhea)
- vomiting
- diarrhea
Physical Exam
Lab Investigations
Samples should be collected with nasopharyngeal swabs or aspirates (instructional video provided).
Real-time PCR is the most effective means of identifying flu strain. Other options include antigen testing, immunofluorescence, or viral culture.
Diagnostic Imaging
Differential Diagnosis
Personal Protection
Key means of avoiding infection include:
- wash hands thoroughly with soap and warm water, or use hand sanitizer
- cough and sneeze in your arm or sleeve
- get your annual influenza shot
- keep doing what you normally do, but stay home if sick
- talk to a health professional if you experience severe influenza-like symptoms.
Treatments
The human swine influenza H1N1 appears to be treatable with antivirals
- oseltamivir (Tamiflu): adults 75 mg twice a day for 5 days; children > 1 year - dosing based on body weight
- zanamivir (Relenza): adults and children >7 years - 10 mg (2 puffs) twice a day for 5 days
It is resistant to amantadine and rimantadine.
Consequences and Course
While many cases resolves after 7-10 days, complications have occasionally been severe. These have included:
- 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
- secondary bacterial pneumonia with or without sepsis.
Evolutionary Pathway
The 1918 Spanish flu began mildly in the spring, dwindled in the summer, and caused disaster in the fall. This has people worried about a similar trajectory this time around.
Resources and References