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Communicability

This study examines the communicability of Severe Acute Respiratory Syndrome (SARS), the factors affecting its transmission, and the effectiveness of precautions in healthcare settings. The results highlight the importance of early identification and isolation of cases, as well as proper infection control practices.

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Communicability

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  1. Communicability • Patient factors • Not infectious prior to symptoms • Increases with increased severity of disease • Increases post-onset symptoms (peak at day 7-10) • Not infectious after recover • No evidence of prolonged carriage or relapse • Setting • Duration, degree of contact • Contact with airway (?contact with stool)

  2. Communicability: time in disease course Peiris et al. Lancet, 2003

  3. Onset (days) 0 – 2 3 – 5 6 – 8 9 – 11 12 – 14 15 – 17 18 – 20 21 – 23 % positive 31 43 60 57 59 35 18 13 NPA / TNS N=392 PCR: Time to positive Stools N=50 %positive 0 57 86 90 100 33 60 43 Public Health - Hong Kong May 2003

  4. Communicability • Patient factors • Not infectious prior to symptoms • Increases with increased severity of disease • Increases post-onset symptoms (peak at day 7-10) • Not infectious after recover • No evidence of prolonged carriage or relapse • Setting • Duration, degree of contact • Contact with airway (?contact with stool)

  5. Exposure Risk in ICU • Loeb et al. (ICAAC 2003) • 8/32 entering room vs 0/11 others (P=0.09) • Risks: assisting with intubation RR=4.2 (1.6, 11) suctioning prior to intubation RR=4.2 (1.6,11) manipulation O2 mask RR=9.0 (1.3,65) • Scales et al. (ICAAC 2003) • 6/31 entering room vs. 1/38 others RR=8.8 (1,420) • Risks: in room for >4 hrs RR=24 (1.2,311) present >30min with NIV RR=105 (3,3000)

  6. SARS Control • Identification of cases • Isolation/quarantine

  7. IP Varia et al. CMAJ 2003

  8. Toronto Area Probable and Suspect cases by source of infection May 5, 2003 12 Travel Non health care Health care settings 10 8 Number of cases (P & S) 6 4 2 0 28-Apr-03 30-Apr-03 02-Apr-03 04-Apr-03 06-Apr-03 08-Apr-03 10-Apr-03 12-Apr-03 14-Apr-03 16-Apr-03 18-Apr-03 20-Apr-03 22-Apr-03 24-Apr-03 26-Apr-03 01-Mar-03 03-Mar-03 05-Mar-03 07-Mar-03 09-Mar-03 11-Mar-03 13-Mar-03 15-Mar-03 17-Mar-03 19-Mar-03 21-Mar-03 23-Mar-03 25-Mar-03 27-Mar-03 29-Mar-03 31-Mar-03 23-Feb-03 25-Feb-03 27-Feb-03 02-May-03 04-May-03 Date of onset of first symptoms

  9. Grace Division Emergency Department March 16; 22:45-23:30

  10. Reported cases of SARS in cases linked to the BLD group March 20 to April 16, 2003 8 Health Care Worker 7 BLD Family 6 5 Church meetings Funeral 4 Number of cases Mr. S Jr. 3 2 1 0 19/03/03 21/03/03 23/03/03 25/03/03 27/03/03 29/03/03 31/03/03 02/04/03 04/04/03 06/04/03 08/04/03 10/04/03 12/04/03 14/04/03 16/04/03 Date of onset of symptoms

  11. Cluster of SARS in HCWs • 54 y.o.m. physician • April 1-2 saw 3 patients from BLD community • April 4-5 became ill • April 12 admitted to ICU • April 13 • Intubated • RT-PCR positive in sputum and stool • April 15-21 • 9 HCW become ill including 6 involved with intubation MMWR 2003 May 16

  12. Effectiveness of Precautions • Seto et al. Lancet 2003: Case (n=13)/Control (241) • Lower risk with handwashing OR 0.2 (.07,1) • Lower risk with gloves OR 0.5 (.14,1.6) • Lower risk with gown OR undef (P=.006) • Lower with masks OR 0.08 (.02,.33) • Loeb et al. ICAAC 2003: Cohort (43 nurses, 8 infected) • Lower risk with gloves OR 0.45 (.44, 4.5) • Lower risk with gown OR 0.36 (.10,1.2) • Lower risk with masks OR 0.23 (.07,.78)

  13. Number of SARs hospitalization days Mount Sinai Hospital 31 hours of unprotected exposure (7 staff infected) 338 days of protected exposure (?1 staff infected) March April March

  14. Transmission in the setting of any precautions, Toronto • Phase I - 260 patients • 22 HCW infected • intubation, cardiac arrest, “pre-intubation” care • Phase II – 129 patients • 3 HCW infected • cardiac arrest, bronchoscopy, “pre-intubation” care

  15. Differences between Phase I and Phase II • HCW training and awareness • “Enhancements” • Double gloves, hair & foot covering, greens • Practice issues • Minimize time in room • Minimize contact with patient • Medical therapy to reduce cough/vomiting • Minimize procedures that increase risk of droplets

  16. Protective Barriers: N95 masks, face shields, gown and gloves

  17. Phase II What went wrong?

  18. Relaxation of precautions

  19. Impact on NYGH • HCWs 39 • Patients 30 • Visitors 18

  20. Conclusions • Disease driven by exposure • Transmission • Primarily in health care settings • Droplet/contact • Heterogeneous between patients • Control • Unrecognized patients are the most important problem • Precautions include not only barriers, but also practice • Compliance with precautions is critical

  21. Acknowledgements Allison McGeer and Karen Green The staff and patients of greater Toronto area hospitals and public health departments

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