Summary and Impact of the 2012-2013 Influenza Season Steve Forest, - PDF document

10/3/2013 Summary and Impact of the 2012-2013 Influenza Season Steve Forest, MPH Epidemiology Research Associate Allegheny County Health Department Objectives • Explain the epidemiology of seasonal influenza • Discuss the 2012-13 influenza season from a national and state perspective • Describe the 2012-13 influenza season impact on Allegheny County Summary and Impact of the 2012-2013 Influenza Season INFLUENZA REVIEW 1

10/3/2013 What is Influenza? • Highly infectious viral illness • Single-stranded RNA virus of the Orthomyxoviridae family • 3 types: A,B,C • Subtypes of type A determined by hemagglutinin (H) and neuraminidase (N) – H1, H2, and H3 have a role in virus attachment to cells – N1 and N2 have a role in virus penetration into cells Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases. Atkinson W, Wolfe S, Hamborsky J, eds. 12th ed., second printing. Washington DC: Public Health Foundation, 2012. Influenza Virus Strains • Type A – humans and other animals – moderate to severe illness – all age groups – Has subtypes determined by surface antigens hemagglutinin and neuraminidase – H1N1 and H3N2 have co-circulated since 1977 • Type B – humans only – milder disease – primarily affects children • Type C – rarely reported in humans – no epidemics Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases. Atkinson W, Wolfe S, Hamborsky J, eds. 12th ed., second printing. Washington DC: Public Health Foundation, 2012. Influenza Virus Nomenclature • The nomenclature to describe the type of influenza virus is expressed in this order: – 1) virus type – 2) geographic origin – 3) strain number – 4) year of isolation – 5) virus subtype Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases. Atkinson W, Wolfe S, Hamborsky J, eds. 12th ed., second printing. Washington DC: Public Health Foundation, 2012. 2

10/3/2013 Influenza Clinical Features • Incubation period 2 days (range 1-4 days) • In general, only about 50% of infected persons will develop the classic clinical symptoms of influenza which includes: – Abrupt onset of fever, muscle aches, sore throat, nonproductive cough, headache • Severity of illness depends on prior experience with related variants Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases. Atkinson W, Wolfe S, Hamborsky J, eds. 12th ed., second printing. Washington DC: Public Health Foundation, 2012. Influenza Complications • Most Commonly – Secondary bacterial pneumonia – Exacerbation of underlying chronic health conditions • Less Commonly – Primary viral pneumonia – Reye syndrome – Myocarditis • Death 5-10 per 10,000 cases Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases. Atkinson W, Wolfe S, Hamborsky J, eds. 12th ed., second printing. Washington DC: Public Health Foundation, 2012. Impact of Influenza • Highest rates of complications and hospitalization among young children and adults > 64 years • On average, >200,000 hospitalizations per year and 23,000 deaths are related to influenza • 90% of flu-related deaths occur in adults older than 64 years • Greater number of hospitalizations during type A (H3N2) epidemics • The cost of a severe epidemic has been estimated to be $12 billion Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases. Atkinson W, Wolfe S, Hamborsky J, eds. 12th ed., second printing. Washington DC: Public Health Foundation, 2012. 3

10/3/2013 Month of Peak Influenza Activity United States, 1976-2008 Vaccination Schedule • Optimal time to vaccinate is BEFORE flu activity picks up in community • Adults achieve peak antibody protection in 2 weeks • Vaccine may be given as soon as it is available • Providers should continue to offer vaccine throughout flu season Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases. Atkinson W, Wolfe S, Hamborsky J, eds. 12th ed., second printing. Washington DC: Public Health Foundation, 2012. Flu Vaccine Effectiveness • Flu vaccine effectiveness is affected by: – Similarity of the vaccine strains to the circulating strains – Age and health status of the recipient • Flu vaccines are effective in protecting against illness up to: – 90% of healthy people ages 6 months to 64 years – 30-40% of adults older than 64 years • Among adults older than 64 years, the vaccine is: – 50%–60% effective in preventing hospitalization – 80% effective in preventing death Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases. Atkinson W, Wolfe S, Hamborsky J, eds. 12th ed., second printing. Washington DC: Public Health Foundation, 2012. 4

10/3/2013 2012-13 Flu Vaccine Effectiveness • Overall, in 2012-13, influenza vaccination reduced the risk for medical visits resulting from – Influenza A and B by 56% – Influenza A (H3N2) alone by 47% – Influenza B alone by 67% • The preventive benefits against influenza B were consistent across all age groups • The preventive benefits against influenza A (H3N2) viruses also were largely consistent for persons aged 6 months–64 years, but the benefit was not significant among adults over 64 years • Nevertheless, flu vaccine still remains the best preventive tool available Centers for Disease Control and Prevention. Interim Adjusted Estimates of Seasonal Influenza Vaccine Effectiveness – United States, February 2013. MMWR 2013;62:119-123. Laboratory Diagnosis of Flu • A flu infection cannot be diagnosed accurately on signs and symptoms alone, lab testing can confirm the diagnosis • Molecular detection (PCR) – Considered the gold standard for influenza diagnosis – RT-PCR is the most sensitive method for the detection of influenza virus • Virus isolation (culture) and rapid culture assays – Allows for full antigenic characterization, which is needed for determining vaccine match – Requires an average of 4.5 days to obtain results – Rapid culture assays can produce results in 18–40 hours Centers for Disease Control and Prevention. Manual for the surveillance of vaccine-preventable diseases. Centers for Disease Control and Prevention, Atlanta, GA, 2008. Laboratory Diagnosis of Flu • Antigen detection (Rapid Influenza Diagnostic Test) – Results are available in as little as 15 minutes – RIDT are not very accurate when flu incidence in the community is low • Serology (antibody tests) – Requires paired serum specimens collected several weeks apart – Nowadays there is no clinical utility to these tests – they should not be done – Diagnosis of influenza CANNOT be made from a single serum sample Centers for Disease Control and Prevention. Manual for the surveillance of vaccine-preventable diseases. Centers for Disease Control and Prevention, Atlanta, GA, 2008. 5

10/3/2013 Lab Based Surveillance • Three main types of labs: – Commercial (Quest Diagnostics, LabCorp, etc.) – Hospital-based – Public Health Laboratories • Labs provide confirmation of RIDTs • Some labs test for novel or variant strains • Labs report positive test results to PA-NEDSS PA-NEDSS • PA-NEDSS electronically transmits disease reports from hospitals, laboratories, and physicians to state, district, county and municipal health departments • This surveillance system helps control flu by: – Monitoring prevalence of circulating strains – Detecting new strains for vaccine formulation – Estimating influenza-related morbidity, mortality and economic loss – Rapidly detecting outbreaks • ACHD investigates positive flu cases who are hospitalized, died, or pregnant, or live in a Long-Term Care Facility (LTCF) Centers for Disease Control and Prevention. Manual for the surveillance of vaccine-preventable diseases. Centers for Disease Control and Prevention, Atlanta, GA, 2008. Confirmed vs. Suspect • In Allegheny County, positive flu cases that are investigated are further classified as confirmed or suspect – Confirmed • Tested positive via culture or PCR – Suspect • Tested positive via Rapid Influenza Diagnostic Test 6

10/3/2013 Please keep in mind that laboratory-confirmed cases represent only a fraction of the total public health burden of influenza, as most people with the flu are diagnosed and treated empirically and do not have lab tests performed to determine the cause of their illness. Summary and Impact of the 2012-2013 Influenza Season INFLUENZA SURVEILLANCE – UNITED STATES 7

10/3/2013 National Baseline Summary and Impact of the 2012-2013 Influenza Season INFLUENZA SURVEILLANCE – PENNSYLVANIA 8

10/3/2013 Week 3 Source: http://www.portal.state.pa.us/portal/server.pt/document/1353506/2012_13_season_data_pdf Flu Impact - Pennsylvania • For the 2012-13 flu season, the Pennsylvania Department of Health reported: – 44,00 lab positive flu cases – 3,600 hospitalizations – 200 deaths – 560 outbreaks of influenza in long-term care facilities resulting in more than 3,000 illnesses and 100 deaths among adults older than 64 years Source: http://www.portal.state.pa.us/portal/server.pt/document/1353506/2012_13_season_data_pdf 2009-10 Flu Season 2012-13 Flu Season Source: http://www.portal.state.pa.us/portal/server.pt/document/1353506/2012_13_season_data_pdf 9