Outbreak Investigation and Control

Transcription

1 Outbreak Investigation and Control Tomás J. Aragón, MD, DrPH Health Officer, City & County of San Francisco Director, Population Health Division (PHD) San Francisco Department of Public Health Adjunct Faculty, Division of Epidemiology UC Berkeley, School of Public Health Blog: November 18, 2013 Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Outbreak Investigation and Control 1 Introduction 2 Transmission dynamics Transmission containment 3 Outbreaks investigations 4 Outbreak case studies Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

2 Introduction Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 What is a cluster? outbreak? epidemic? pandemic? Cluster A cluster is an observed increase in cases concentrated in time or space. A cluster may or may not represent an outbreak. Outbreak An outbreak is the occurrence of more cases than would be expected for a time and place. Epidemic An epidemic is outbreak that is more widespread and sustained. Pandemic A pandemic is a global epidemic. Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

3 Well established cause of outbreaks! Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Well established response to outbreaks! Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

4 Why do we investigate outbreaks? Prevent additional cases in the current outbreak Prevent future outbreaks Learn about a new disease Learn something new about an old disease Reassure the public Minimize economic and social disruption Training (e.g., teach epidemiology) Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Concepts for controlling infectious diseases 1 Chain model of infectious diseases 2 Natural history of infection and infectiousness 3 Convergence model of microbial threats Transmission dynamics 1 Reproductive number 2 Infection rate among susceptibles 3 Generation time Transmission containment 1 Control points, strategies, and measures Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

5 Chain model of infectious diseases Mode of Transmission Microbial Agent in Reservoir or Source Susceptible Host Portal of Exit Portal of Entry Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Chain model Reservoirs / Sources 1 Human 2 Animals (zoonoses) 3 Environment A reservoir can always be a source, but not all sources are reservoirs. Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

6 Chain model Modes of Transmission 1 Contact Direct contact (e.g., touching, kissing, having sex) Indirect contact (e.g., intermediate object, fomites) 2 Respiratory droplets (large particles: secrections, cough, sneeze) 3 Airborne (small particles: droplet nuclei, dust) 4 Vehicle-borne (e.g., ingestion, instrumentation, infusion/injection) 5 Vector-borne (e.g., mechanical, biologic) 6 Vertical transmission (e.g., in utero, at birth, breast milk) Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Portal of exit and entry Mucous membrane surfaces Nose, mouth, oropharynx Gastrointestinal tract Genitourinary tract Respiratory tract Anorectum Skin (or skin penetration) Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

7 Good infection control starts with common sense: Cover the source! Source: American Society of Microbiology Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Disease scare at San Jose airport: 5 on flight from Asia examined none found with SARS I San Francisco Chronicle, Wednesday, April 2, 2003 In a false alarm heard round the world, the Santa Clara County health system jumped into high alert Tuesday morning when an American Airlines flight from Tokyo radioed that it might have five cases of the mysterious flulike illness known as SARS on board. [Joan] Krizman said she had no hard feelings about being treated as a potential health threat. The couple had just completed an exhausting, monthlong journey that included stops in Vietnam, Thailand and Hong Kong three Southeast Asian hot spots for SARS. There were four fire trucks and eight police cars and four or five ambulances, she recalled. I couldn t believe it. I thought, Wow! What s going on here? Little did I know that we were to be the victims. Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

8 Disease scare at San Jose airport: 5 on flight from Asia examined none found with SARS II The couple were asked twice to go to Valley Medical Center, and twice they politely declined. And then, Krizman said, they soon opened up the ambulance doors and said, sorry, we re taking you to the hospital. At the hospital, according to Krizman, we were the only ones there not wearing masks. When word got out just who they were, she said, People started running like crazy, like we were the bubonic plague. They put us in a room full of people with plastic boots and face shields and masks. Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Nurse wearing N-95 respirator outside of intensive care unit Associated Press: In a ward at Sunnybrook and Womens Hospital in Toronto, a nurse waits outside the door of a patient diagnosed with the illness [SARS]. Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

9 Public-devised infection control, SARS outbreak, 2003 Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Infection control practices, SARS outbreak, 2003 Reuters: An Indian woman diagnosed with SARS sits on her bed at the Doctor Naidu Infectious Diseases Hospital in the western city of Pune. Doctors reported India s first case of the disease in a marine engineer from the western coastal state of Goa on Friday, April 18, Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

10 Natural history of infection and infectiousness (A vs. B) A Time of infection Symptomatic, Not infectious Susceptible Latent period Infectious period Non-infectious Incubation period Symptomatic period Non-diseased B Time of infection No symptoms, Infectious Susceptible Latent period Infectious period Non-infectious Incubation period Symptomatic period Non-diseased When the latent period is shorter than the incubation period (B), an infected person becomes infectious before symptom onset. Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Convergence model for human-microbe interaction Institute of Medicine. Microbial threats to health: Emergence, Detection, and Response. National Academy Press, 2003 Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

11 Transmission dynamics Epidemic curve in action, SARS outbreak, 2003 Number of probable cases of severe acute respiratory syndrome, by date of fever onset and reported source of infection, Singapore, Feb 25-Apr 30, Source: CDC MMWR (2003) PMID: Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Transmission dynamics Reproductive number in action, SARS outbreak, 2003 Probable cases of severe acute respiratory syndrome, by reported source of infection, Singapore, Feb 25-Apr 30, Source: CDC MMWR (2003) PMID: Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

12 Transmission dynamics In Contagion, Dr. Erin Mears (Kate Winslet) explans R 0 Contagion is a 2011 public health thriller directed by Steven Soderbergh. Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Transmission dynamics Reproductive number vs. Infection rate in susceptibles REPRODUCTIVE NUMBER (R) Contact Rate (c) INFECTON RATE (I) Microbial Agent in Reservoir or Source Susceptible Host Fraction of population that is infectious (P) Duration of Infectiousness (d) R(t) = (R0) x(t) = (d c p) x(t) Transmission Probability (p) Fraction of population that is susceptible (x) I(t) = c p P(t) Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

13 Transmission containment Transmission containment Control strategies 1 Reduce contact rate (c) 2 Reduce fraction of population that is infectious (P ) 3 Reduce biological infectiousness (affects p) 4 Reduce biological susceptibility (affects p) 5 Interrupt transmission (physical, chemical) (affects p) 6 Reduce fraction of population that is susceptible (x) Control measures... are interventions designed to address control strategies. Always consider mutliple perspectives: host, agent, infectious sources, and environment (physical, social, economic, political, etc.) Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Transmission containment Reducing the contact rate (example) Case isolation (infectious) Quarantine (exposed) Sheltering (not exposed) Social distancing (status unkown) Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

14 Investigation How to investigate an outbreak in 7 steps (or less) 1 Case investigation 2 Cause investigation 3 Control measures 4 Conduct analytic study (if necessary) 5 Conclusions (causal inference) 6 Continue surveillance 7 Communicate findings To see alternative approach visit CDC at Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Investigation Step 1: Case investigation Confirm outbreak Establish preliminary causal hypotheses Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

15 Investigation Step 2: Cause investigation Systematically review known causal factors Laboratory (microbe) Epidemiologic/Clinical/Infection Control (host) Veterinary & Vectorbore Environmental Law enforcement/ Forensics Prioritize likely causes to guide control measures (Step 3) Generate testable hypotheses to conduct analytic study (Step 4) if cause remains unknown or control measure not working Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Investigation Step 3: Control measures (do early) Containment using epidemiologic concepts and dynamics Organization of control measures Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

16 Investigation Step 4: Conduct analytic study if... Outbreak continues No cause is implicated Control measures ineffective Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Investigation Transmission of the SARS on Aircraft, 2003 Figure : Schematic Diagram of the Boeing Aircraft on Flight 2 from Hong Kong to Beijing. Below is 2 2 table for retrospective cohort study SARS case Exposure Yes No Total Yes No Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

17 Investigation Retrospective cohort study to assess mode of transmission Risk ratio R 1 (t) = 8 23 R 0 (t) = RR = 8/23 10/88 = 3.1 (95% CI, ; p = 0.02) Odds ratio O 1 (t) = 8 15 O 0 (t) = (D)OR = 8/15 10/77 = 4.1 (95% CI, ; p = 0.02) Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34 Case studies Selected Case Studies from San Francisco Tomás J. Aragón, MD, DrPH (SFDPH) Outbreak Investigation and Control November 18, / 34

18 The CIDER Model of Infectious Diseases A. Microbial agent D. Portal(s) of exit F. Portal(s) of entry B. Reservoir(s) C. Source(s) Air 2. Water 3. Food 4. People 5. Animals & Vectors 6. Vehicles (others) 7. Soil & debris E. Modes of transmission Direct contact 2. Indirect contact 3. Droplets 4. Airborne 5. Vehicle-borne 6. Vector-borne 7. Vertical G. Susceptible hosts (The 7 Habits of Uninfected People) Safe consumption 2. Personal hygiene 3. Cover your cough 4. Get vaccinated 5. Use protection 6. Reduce special risks 7. Infection control UC Berkeley Center for Infectious Diseases & Emergency Readiness (CIDER), 2008