The 2009 H1N1 flu pandemic or swine flu was an influenza pandemic, and occurred against a backdrop of pandemic response planning at all levels of government including
The 2009 flu pandemic or swine flu was an influenza pandemic, and the second of the two pandemics involving H1N1 influenza virus (the first of them being the 1918 flu pandemic), albeit in a new version. First described in April 2009, the virus appeared to be a new strain of H1N1 which resulted when a previous triple reassortment of bird, swine and human flu viruses further combined with a Eurasian pig flu virus, leading to the term "swine flu".
Unlike most strains of influenza, H1N1 does not disproportionately infect adults older than 60 years; this was an unusual and characteristic feature of the H1N1 pandemic. Even in the case of previously very healthy people, a small percentage will developpneumonia or acute respiratory distress syndrome (ARDS). This manifests itself as increased breathing difficulty and typically occurs 3–6 days after initial onset of flu symptoms.The pneumonia caused by flu can be either direct viral pneumonia or a secondary bacterial pneumonia. In fact, a November 2009 New England Journal of Medicine article recommends that flu patients whose chest X-ray indicates pneumonia receive both antivirals and antibiotics. In particular, it is a warning sign if a child (and presumably an adult) seems to be getting better and then relapses with high fever, as this relapse may be bacterial pneumonia.
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| the outbreak of swine flu near Sannomiya JR station May 20, 2009, in Kobe, Japan. |
The swine-flu pandemic of 2009 may have killed up to 203,000 people worldwide—10 times higher than the first estimates based on the number of cases confirmed by lab tests, according to a new analysis by an international group of scientists.
The researchers also found almost 20-fold higher rates of respiratory deaths in some countries in the Americas than in Europe. Looking only at deaths from pneumonia that may have been caused by the flu, they found that Mexico, Argentina and Brazil had the highest death rates from the pandemic in the world. The toll was far lower in New Zealand, Australia and most parts of Europe, according to the study, published today (Nov. 26) in the journal PLOS Medicine.
The new estimates are in line with a previous study published last year that used a different statistical strategy to evaluate the impact of the pandemic caused by the H1N1 virus. However, that study, which was done before countries' data on overall death rates in 2009 had become available, found that the majority of deaths occurred in Africa and Southeast Asia.
Signs and symptoms
The symptoms of H1N1 flu are similar to those of other influenzas, and may include fever, cough (typically a "dry cough"), headache, muscle or joint pain, sore throat, chills,fatigue, and runny nose. Diarrhea, vomiting, and neurological problems have also been reported in some cases. People at higher risk of serious complications include those aged over 65, children younger than 5, children with neurodevelopmental conditions, pregnant women (especially during the third trimester), and those of any age with underlying medical conditions, such as asthma, diabetes, obesity, heart disease, or a weakened immune system (e.g., taking immunosuppressive medications or infected with HIV). More than 70% of hospitalizations in the U.S. have been people with such underlying conditions, according to the CDC.In September 2009, the CDC reported that the H1N1 flu "seems to be taking a heavier toll among chronically ill children than the seasonal flu usually does." Through 8 August 2009, the CDC had received 36 reports of paediatric deaths with associated influenza symptoms and laboratory-confirmed pandemic H1N1 from state and local health authorities within the United States, with 22 of these children having neurodevelopmental conditions such as cerebral palsy, muscular dystrophy, or developmental delays. "Children with nerve and muscle problems may be at especially high risk for complications because they cannot cough hard enough to clear their airways". From 26 April 2009, to 13 February 2010, the CDC had received reports of the deaths of 277 children with laboratory-confirmed 2009 influenza A (H1N1) within the United States.
Severe cases
The World Health Organization reports that the clinical picture in severe cases is strikingly different from the disease pattern seen during epidemics of seasonal influenza. While people with certain underlying medical conditions are known to be at increased risk, many severe cases occur in previously healthy people. In severe cases, patients generally begin to deteriorate around three to five days after symptom onset. Deterioration is rapid, with many patients progressing to respiratory failure within 24 hours, requiring immediate admission to an intensive care unit. Upon admission, most patients need immediate respiratory support with mechanical ventilation.
A November 2009 CDC recommendation stated that the following constitute "emergency warning signs" and advised seeking immediate care if a person experiences any one of these signs:
In adults:
- Difficulty breathing or shortness of breath
- Pain or pressure in the chest or abdomen
- Sudden dizziness
- Confusion
- Severe or persistent vomiting
- Low temperature
In children:
- Fast breathing or working hard to breathe
- Bluish skin color
- Not drinking enough fluids
- Not waking up or not interacting
- Being so irritable that the child does not want to be held
- Flu-like symptoms which improve but then return with fever and worse cough
- Fever with a rash
- Being unable to eat
- Having no tears when crying
Research later indicated that the severe flu effects in healthy young and middle-aged adults are caused by an excessive immune response.
Complications
Most complications have occurred among previously healthy individuals, with obesity and respiratory disease as the strongest risk factors. Pulmonary complications are common. Primary influenza pneumonia occurs most commonly in adults and may progress rapidly to acute lung injury requiring mechanical ventilation. Secondary bacterial infection is more common in children. Staphylococcus aureus, including methicillin-resistant strains, is an important cause of secondary bacterial pneumonia with a high mortality rate;streptococcus pneumoniae is the second most important cause of secondary bacterial pneumonia for children and primary for adults. Neuromuscular and cardiac complications are unusual but may occur.A United Kingdom investigation of risk factors for hospitalisation and poor outcome with pandemic A/H1N1 influenza looked at 631 patients from 55 hospitals admitted with confirmed infection from May through September 2009. 13% were admitted to a high dependency or intensive care unit and 5% died; 36% were aged <16 years and 5% were aged ≥65 years. Non-white and pregnant patients were over-represented. 45% of patients had at least one underlying condition, mainly asthma, and 13% received antiviral drugs before admission. Of 349 with documented chest x-rays on admission, 29% had evidence of pneumonia, but bacterial co-infection was uncommon. Multivariate analyses showed that physician-recorded obesity on admission and pulmonary conditions other than asthma or chronic obstructive pulmonary disease (COPD) were associated with a severe outcome, as were radiologically confirmed pneumonia and a raised C-reactive protein (CRP) level (≥100 mg/l). 59% of all in-hospital deaths occurred in previously healthy people.
Fulminant (sudden-onset) myocarditis has been linked to infection with H1N1, with at least four cases of myocarditis confirmed in patients also infected with A/H1N1. Three out of the four cases of H1N1-associated myocarditis were classified as fulminant, and one of the patients died. Also, there appears to be a link between severe A/H1N1 influenza infection and pulmonary embolism. In one report, five out of 14 patients admitted to the intensive care unit with severe A/H1N1 infection were found to have pulmonary emboli.
An article published in JAMA in September 2010 challenged previous reports and stated that children infected in the 2009 flu pandemic were no more likely to be hospitalised with complications or get pneumonia than those who catch seasonal strains. Researchers found that about 1.5% of children with the H1N1 swine flu strain were hospitalised within 30 days, compared with 3.7% of those sick with a seasonal strain of H1N1 and 3.1% with an H3N2 virus.
Diagnosis
The CDC criteria for suspected H1N1 influenza are as follows[2] :Onset of acute febrile respiratory illness within 7 days of close contact with a person who has a confirmed case of H1N1 influenza A virus infection, or
Onset of acute febrile respiratory illness within 7 days of travel to a community (within the United States or internationally) where one or more H1N1 influenza A cases have been confirmed, or
Acute febrile respiratory illness in a person who resides in a community where at least one H1N1 influenza case has been confirmed.
