Influenza A H1 N1
* Influenza Virus Types A and BType A(Seasonal, avian, swine influenza,….) Type B (Seasonal influenza)
Can cause significant disease
Generally causes milder disease but may also cause severe disease
Infects humans and other species (e.g., birds; H5N1)
Limited to humans
Can cause epidemics and pandemics (worldwide epidemics)
Generally causes milder epidemics
While there are three types of influenza viruses—A, B, and C—only two cause significant disease in humans (A and B). Type B influenza viruses are limited to humans, whereas Type A viruses can cause severe disease in humans and affect more species. Influenza Type A Type A influenza is considered to cause the most serious disease among the influenza viruses, although not all strains cause clinical disease. Influenza A can cause severe epidemics (as well as severe worldwide epidemics; or pandemics) among all ages. Influenza type A infects multiple species including people, birds, pigs, horses, and other animals. Wild birds are the natural hosts for these viruses.
Influenza Type B Influenza B viruses are usually found only in humans. Influenza B viruses can cause some morbidity and mortality among humans, but in general are associated with less severe epidemics (chiefly among children) than influenza A viruses. Although influenza type B viruses can cause human epidemics, they have not caused pandemics. Because avian influenza and all pandemic viruses are of the Type A variety, we will focus this session on Type A influenza viruses.
1920 1940 1960 1980 2000
H1N1H2N2
H3N2
1918: “Spanish Flu” 1957: “Asian Flu” 1968: “Hong Kong Flu” 20-40 million deaths
1-4 million deaths
1-4 million deaths
Pandemic Waves (1918-1919)
Seasonal Influenza A public health problem each year Usually some immunity built up from previous exposures to the same subtypeInfants and elderly most at risk
Influenza Pandemics Appear in the human population rarely and unpredictably Human population lacks any immunityAll age groups, including healthy young adults
Seasonal Epidemics vs. PandemicsWhile seasonal influenza occurs every year, pandemic influenza rarely occurs. Here we compare some features of seasonal influenza with features of pandemic influenza. While the population usually has some immunity built up from previous exposures to seasonal influenza, the human population lacks any immunity to pandemic influenza strains.
In seasonal influenza epidemics, infants and the elderly are most at risk of illness and complications. But during an influenza pandemic, even healthy, young people are at increased risk for serious complications. Seasonal influenza strains are the result of Antigenic Drift, while pandemic influenza strains are the result of Antigenic Shift.
The new virus must be efficiently transmitted from one human to another
Prerequisites for pandemic influenzaA new influenza virus emerges to which the general population has little/no immunity
The new virus must be able to replicate in humans and cause disease
2 of the 3 prerequisites for a human pandemic have been met A novel influenza virus has emerged and the general population has demonstrated little or no immunity And the new virus has been able to replicate in humans. The main questions that remains are: Will the virus will develop into a form that is efficiently transmitted from one human to another? (thus meeting the criteria for a pandemic) If so, where, when, how quickly, and how severely?
The first two of three prerequisites have been met: A novel virus Virus must be able to replicate in humans and cause disease New virus must be efficiently transmitted from one human to another Virus can improve its transmissibility via two mechanisms: adaptive mutation genetic reassortment (can take place in humans without prior adaptation in another mammalian species, such as the pig)
The InfluenzaVirus
A H1N1 :new virusThe 2009 H1N1 virus is a hybrid of swine, avian and human strains Influenza A (H1N1)
Viral Re-assortment
Reassortment in pigsReassortment in humans
Pandemic Influenza Virus
WHO Pandemic Phases
Big droplets fall on people surfaces bed clothesCourtesy of CDC
Signs and Symptoms
Human InfluenzaType of infection
Upper and lower respiratory
Fever
Yes
Headache
Yes
Cough
Yes
Respiratory symptoms
Varies; sore throat to difficulty breathing
Gastrointestinal symptoms
Uncommon, except children, elderly
Recovery
2-7 days
It can be difficult to tell if a patient has influenza because the signs and symptoms for influenza are similar to those for other diseases that may cause respiratory illnesses. If you do suspect influenza, there are a few differences between human influenza and avian influenza that you can assess, especially in the early days of illness. Human influenza usually causes both upper respiratory (sore throat runny nose) and lower respiratory (cough, bronchitis) symptoms. Common signs and symptoms include fever, headache, cough, sore throat, muscle ache, and exhaustion. Other respiratory symptoms may appear, varying from sore throat to difficulty breathing.
Children and the elderly may also have gastrointestinal symptoms like diarrhea, vomiting and nausea, but adults uncommonly have gastrointestinal symptoms, except loss of apetitie. People generally recover anywhere from 2 to 7 days after symptoms appear. However, cough and muscle ache may last more than 14 days. Although influenza generally causes an upper respiratory infection with tracheobronchitis, it can progress to pneumonia and respiratory failure in some cases.
Although similar initially, avian influenza differs from human influenza in its course. Avian influenza leads to a lower respiratory illness with variable upper respiratory involvement. Initial symptoms are similar to human influenza. These include fever, headache, cough, sore throat, muscle ache, and exhaustion. Gastrointestinal symptoms of watery diarrhea, vomiting, and abdominal pain have been more commonly reported from H5N1 patients (20-70% diarrhea rate depending on case series). Symptoms of a lower respiratory infection appear early in course of the illness.
About five days after symptoms appear, patients often begin to have difficulty breathing leading to respiratory distress, and an increased respiratory rate may also be observed. By this time, cough is prominent, sputum production may occur sometimes containing blood. Most patients develop pneumonia with bilateral pulmonary infiltrates.
Swine flu
"The entire purpose is to limit exposure“The Centers for Disease Control and Prevention hopes to have a vaccine to manufacturers within 6 months (??)Non-pharmaceutical Interventions
1. Delay disease transmission and outbreak peak 2. Decompress peak burden on healthcare infrastructure 3. Diminish overall cases and health impactsDaily Cases
#1
#2
#3
Days since First Case
Pandemic outbreak: No intervention
Pandemic outbreak: With intervention
Cough etiquette
Respiratory etiquette Cover nose / mouth when coughing or sneezing Hand washing!Voluntary Isolation
Separation and restricted movement of ill persons with contagious disease (often in a hospital setting and Primarily individual level) Isolate severe and mild cases Location of isolation (home, hospital) depends on several factors (severity of illness, the number of affected persons, the domestic setting) Do not wait for lab confirmation Plan for large number of severe cases Provide medical and social careVoluntary Quarantine
Separation and restricted movement of well persons presumed exposed Identification of contacts Often at home, but may be designated residential facility or hospital Applied at the individual or community level Regular health monitoring is essential part of quarantine Self-health monitoring and reportingHand Washing
Method Wet hands with clean (not hot) water Apply soap Rub hands together for at least 20 seconds Rinse with clean water Dry with disposable towel or air dry Use towel to turn off faucetAlcohol-based Hand Rubs
Effective if hands not visibly soiled More costly than soap & water Method Apply appropriate (3ml) amount to palms Rub hands together, covering all surfaces until dryPatients Cared for at Home
Potential for transmissionMust educate family caregiversFever / symptom monitoringInfection control measuresHand washingUse of available material as mask …Isolation Precautions
Source: Rosie Sokas, MD MOH UIL at Chicago
Droplet precautions: Surgical Masks