Infectious Disease Epidemiolog
A Presentation on:
Epidemiology of Influenza Prabesh Ghimire
This presentation will cover
What is Influenza Influenza Virus Antigenic shift and antigenic drift Epidemiology of H1N1 Influenza
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Epidemiological Burden (Global, Regional and National) Epidemiological Determinants (Agent, Host & Env Factors) Mode of Transmission Clinical Features Diagnosis Management Prevention & Control National Response
What is Influenza?
Highly infectious viral illness Acute respiratory disease
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Upper respiratory tract Lower respiratory tract
Influenza Virus
Single stranded RNA virus Orthomyxoviridae family 3 types: A,B, C Type A- moderate to severe illness
Type B- milder disease
Primarily affects children Humans only
Type C- rarely reported in humans
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All age groups Humans and other animals
No epidemics
Influenza A Virus
Characterized by 2 main surface glycoproteins
Hemagglutinin (HA)- 16 subtypes Neuraminidase (NA)- 9 subtypes
Influenza A virus subtypes classified based on combinations of HA and NA subtype All the subtypes can affect birds (natural hosts) Only a few subtypes capable of infecting humans Important subtypes of public health importance
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H5N1 Influenza A virus Pandemic H1N1 Influenza A virus
Antigenic Shift and Antigenic Drift
Influenza A viruses are dynamic and can evolve by two processes:
Antigenic drift
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Occurs by point mutations in the two genes coding for HA and NA Causes minor changes in surface proteins leads to a new strain which is not recognized by antibodies to previous influenza strains.
Antigenic shift Major change through genetic reassortment Produces a novel influenza A subtype in humans Occurs through mixing of human and animal influenza A virus genes or by animal to human transmission May cause pandemics
H1N1 Influenza (Swine Flu)
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H1N1 Influenza
Novel strain due to antigenic shift Evolved from a reassortant between triple reassortant swine influenza viruses in North American pigs and influenza A virus circulating in Eurasian pigs April 2009: WHO declared the emergence of human cases of H1N1 swine influenza virus 11 June 2009: WHO raised the pandemic alert (phase 5 to 6)
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Epidemiological Burden Global
Till May 2010: >214 countries reported lab confirmed influenza H1N1 2009, including over 18097 deaths
pandemic (Source WHO)
SEAR
Till May 2010: 1808 deaths As of 19 October 2009, in the WHO Southeast Asia region, 10 of 11 member countries have reported 41 513 cases of H1N1 virus infection and 573 deaths. The 3 hardest hit countries in the region were Thailand, India and Indonesia
(Source WHO)
Nepal
Jun 2009: First detection in human specimen collected at TIA Till May 2010: Total no. of confirmed positive cases- 172 Till May 2010: Total death cases -3. All were Female patients (Source NPHL)
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Epidemiological Determinants
Causative agent: Influenza A virus
Host Factors
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Pandemic
H1N1
(2009)
Occurs in every age-group. Population does not have immunity to virus Complications higher in people with underlying diseases such as asthma, cardiac diseases, renal diseases and in pregnancy. Obesity has also found to predispose to severe disease
Environment
Influenza viruses are highly resilient in the environment. Low temperature and low humidity favor aerosol transmission, explaining the seasonal nature of influenza in temperate climates. In tropical climates influenza infections are associated with increased rainfall The best environment for a novel virus is a population without pre-existing immunity to it, enabling it to spread pandemically
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Mode of Transmission
Through droplets from coughing or sneezing, and Through direct or indirect contact with the respiratory secretions of an infected person
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Food is not yet known to be a vehicle for the transmission The secondary attack rate in households:18% to 30%
Incubation Period
Between 1 and 7 days
Period of Communicability
From a day prior to onset of symptoms till after 24 hours after symptoms have subsided.
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Clinical Features
Ranging from mild self-limiting upper respiratory illness to lower respiratory infection including ARDS, cardiac involvement, neurological involvement, multiorgan failure, septicemia and death. Common features: mild respiratory illness with fever, cough, sore throat, dyspnea, rhinorrhea, myalgias, chills, headache and fatigue. Diarrhea and vomiting are more commonly seen than with seasonal flu. Reported complications: myocarditis, pericarditis, encephalitis, seizures, myositis, multiorgan failure and toxic shock syndrome 15
Diagnosis
Reverse-transcriptase polymerase chain reaction (RT-PCR) provides the most timely and sensitive evidence of infection. Clinical diagnosis (based on acute onset of fever and cough) can be increasingly predictive of infection as the prevalence of infection increases.
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Case Management
Hospitalization and antiviral therapy not required for most patients Supportive care includes antipyretics such as paracetamol or acetaminophen, for fever or pain, and fluids, as needed. The virus is currently susceptible to neuraminase inhibitors (oseltamivir and zanamivir).Oseltamivir is believed to reduce the severity and duration of the illness, and might contribute to preventing its progression to severe disease and death. Antiviral therapy may be beneficial especially for pregnant patients, patients with progressive lower respiratory tract disease or pneumonia, and those with underlying medical conditions 17
Prevention and Control Measures
Non-Pharmacological Interventions
Personal protective measures
Isolation and social distancing
Shielding one’s mouth and nose while coughing or sneezing, Frequently washing one’s hands with soap Home quarantine School closure and cancellation of mass gathering
Pharmacological Interventions
Chemoprophylaxis
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If the likelihood of complications is high, oseltamivir or zanamivir may be used as post-exposure chemoprophylaxis for affected individuals, especially healthcare workers
Prevention and Control Measures contd.
Pharmacological Interventions
Vaccination
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Vaccine against the H1N1 virus is presently available in a few countries. Commercial production is about to commence. The first priority of all countries should be to immunize their healthcare workers The next priority should be pregnant women. Inactivated non-adjuvant vaccines similar to most seasonal influenza vaccines are considered the preferred option.
National Response
National Influenza Surveillance Network (10 sentinel sites) Molecular diagnostic assay based influenza surveillance started in 2009 with the introduction of Real-Time PCR (RT-PCR) at National Public Health Laboratory (NPHL) Community spread of Pandemic Influenza A/H1N1 2009 was established in Kathmandu valley on 15 th October, 2009. NPHL designated as National Influenza Centre (NIC) on 19th April, 2010 Influenza Pandemic Preparedness and Response Project (IPPRP) implemented by PAHS under grants from CDC 20
Open Discussion………
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References Narain JP, Kumar R, Bhatia R. Pandemic (H1N1) 2009: epidemiological, clinical and prevention aspects. The National Medical Journal of India. 2009;22(5). Gularia R, Kumar J, Mohan A, Wig N. Influenza A: From highly pathogenic H5N1 to pandemic 2009 H1N1. Epidemiology and clinical features. Indian Journal of Microbiology. 2009;49:315-19. Mpolya EA, Furuse Y, Nukiwa N, Suzuki A, Kamigaki T, Oshitani H. Pandemic (H1N1) 2009 Virus Viewed from an Epidemiological Triangle Model. Journal of Disaster Research. 2009;4(5):1-7.
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WHO. Pandemic (H1N1) 2009 - update 101, [cited 2016 Sep 3], Available from http://www.who.int/csr/don/2010_05_21/en/ CDC. Influenza, [cited 2016 Sep 3], Available from http://www.cdc.gov/vaccines/pubs/pinkbook/flu.html
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