Associate Professor, Dept Pulmonology, JSS Medical College, Mysore
Introduction:
•In April 2009, the World Health Organization (WHO) received reports of sustained person to person infections with a novel influenza A (H1N1) virus in Mexico and the United States.
•Subsequent international spread led WHO to declare on 11 June 2009that the first influenza pandemic in 41 years had occurred.
•This 2009 pandemic H1N1 influenza virus has now spread worldwide, with confirmed cases of pandemic H1N1 virus infection reported in more than 100 countries in all 6 WHO regions.
Earlier major Influenza Pandemics:
•1918: The Spanish flu pandemic remains the most devastating outbreak of modern times. Caused by a form of the H1N1 strain of flu, it is estimated that up to 40% of the world's population were infected, and more than 50 million people died, with young adults particularly badly affected
•1957: Asian flu killed two million people. Caused by a human form of the virus, H2N2, combining with a mutated strain found in wild ducks. The impact of the pandemic was minimized by rapid action by health authorities, who identified the virus, and made vaccine available speedily. The elderly were particularly vulnerable
•1968: An outbreak first detected in Hong Kong, and caused by a strain known as H3N2, killed up to one million people globally, with those over 65 most likely to die
H1N1 Virus
The present Influenza virus developed from a mixing of genetic material of swine, avian and human influenza virus. The mixing of the different influenza strains occurred in the pigs. When there is a gross change in the genetic composition of the virus it is called as ‘antigenic shift’. Once the virus was transmitted to humans, subsequent transmission has occurred from human to human and has resulted in the present pandemic. There has been a resurgence in the number of cases and deaths due to H1N1 with 1000 patients dying of the disease in one week alone.
In an interesting study on how this pandemic virus interacts with other flu viruses, three different flu viruses were competed against the H1N1 inside ferrets
The study demonstrated that H1N1 is clearly superior to other influenza viruses.
–Replicates twice as fast as other viruses
–Spreads deeper into the lungs whereas other viruses were still in the nasal passages
–More communicable
–Did not show any signs of mixing with other strains to create a super bug
Clinical Presentation of Swine Flu:
The clinical presentation of Swine flu can vary between being asymptomatic to a florid pneumonia with ARDS and multi organ failure. The clinical diagnosis of Swine flu is suspected by epidemiological data and confirmed by laboratory methods. However, the initial treatment should not be withheld pending laboratory reports. Uncomplicated Swine flu presents with fever, cough, sore throat, rhinorrhea, myalgia, malaise. No breathlessness, cyanosis or severe dehydration is observed. Gastrointestinal symptoms like diarrhea and vomiting may be present, especially in children. In complicated cases, dyspnea, tachypnea, hypoxia, radiological pneumonia, severe dehydration is commonly observed. Different target organ involvement including encephalopathy, renal failure, hepatic failure, septic shock, rhabdomyolysis and myocarditis are common. It is also observed that associated co-morbidities like asthma, COPD, diabetes, cardiovascular, hepatic or renal diseases also worsen in these patients with swine flu. Progression from an uncomplicated case to a complicated case can sometimes occur rapidly. An initial period of rhinorrhea and fever progresses to tachypnea, dyspnea, cyanosis, hemoptysis, shock, altered consciousness, drowsy, convulsions, confusion, weakness or even paralysis within a short period and therefore careful observation on stable patients is important until they fully recover. Evidence of sustained viral replication or a complicating bacterial infection is suspected if the fever persists beyond 3 days. In subjects with severe dehydration, decreased activity, lethargy, dizziness and decreased urine Decreased activity, lethargy, dizziness and decreased urine output are usually observed.
Recommendations for treatment from the Government of India
•Category A
–Patients with mild fever plus cough / sore throat with or without body ache, headache, diarrhoea and vomiting
–Do not require oseltamivir
–Monitored for progress and reassessed at 24-48 hours
–No testing for H1N1
–Avoid going out and mixing with people
•Category B (i)
–In addition to all the signs and symptoms mentioned under Category-A, if the patient has high grade fever and severe sore throat
–May require home isolation
–Treat with Oseltamivir
•Category B (ii)
–In addition to all the signs and symptoms mentioned under Category-A, individuals having one or more of the following high risk conditions
–Children less than 5 years old;
–Pregnant women;
–Persons aged 65 years or older;
–Patients with lung diseases, heart disease, liver disease, kidney disease, blood disorders, diabetes, neurological disorders, cancer and HIV/AIDS; Patients on long term cortisone therapy
–Treat with Oseltamivir
•Category C
–Symptoms of category A and/or B
–Breathlessness, chest pain, drowsiness, fall in blood pressure, sputum mixed with blood, bluish discoloration of nails
–Irritability among small children, refusal to accept feed
–Worsening of underlying chronic conditions
–Immediate hospitalization, testing for H1N1 and treatment
Current antiviral susceptibility according to WHO
Key principles guiding selection of antivirals during the H1N1 pandemic
•An antiviral should not be used if it known that the strain is likely to be resistant
•When more than one virus is circulating, more than one antiviral may be used to increase the probability of providing coverage with at least one effective agent
•There should be continual monitoring for drug resistance in the local population
Drugs for treatment
Oseltamivir – 75 mg twice daily
Zanamivir – 10 mg twice daily
Chemoprophylaxis
High risk settings as in Nursing home residents, close contact with a case of swine flu
High gain settings as medical and paramedical personnel taking care of patients with swine flu.
Drugs for Chemoprophylaxis
Oseltamivir – 75 mg once daily
Zanamivir – 10 mg once daily
The following Personal Protection Equipments need to be used by health care workers taking care of patients with H1N1 where there is a risk of aerosol generation as in nebulisation, ventilation and endotracheal suction
Mask - N95 respirator
Gowns
Gloves
Eye protection and face shield
Health care workers not involved in aerosol generation can use a triple layer surgical mask. However, care needs to be taken that the mask should not be reused or used when wet.
One of the most important tools for prevention of infections for health care workers and general population is frequent hand washing.
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