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諾沃克病毒 : 高傳染性的背後 Norovirus: Why is it so infectious?

諾沃克病毒 : 高傳染性的背後 Norovirus: Why is it so infectious?. 香港中文大學防疫研究中心 Centre for Emerging Infectious Diseases CUHK. Norovirus. Norovirus. First identified in 1972 previously called a ‘Norwalk-like virus’ or small round structured virus positive strand RNA viruses high mutation rate

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諾沃克病毒 : 高傳染性的背後 Norovirus: Why is it so infectious?

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  1. 諾沃克病毒: 高傳染性的背後Norovirus: Why is it so infectious? 香港中文大學防疫研究中心 Centre for Emerging Infectious Diseases CUHK

  2. Norovirus

  3. Norovirus • First identified in 1972 • previously called a ‘Norwalk-like virus’ or small round structured virus • positive strand RNA viruses • high mutation rate • high antigenic diversity • 5 genogroups (GI, GII and GIV infect human)

  4. Mode of Transmission • Highly infectious, ≤ 10 virions • Fecal-oral route • Vomitus • Waterborne • Foodborne (esp. seafood) • May generate aerosol in projectile vomiting, but no evidence for transmission via the respiratory tract • Mostly in closed settings: hospital, elderly home, healthcare institution, school, food premise, and more Source: CDC Technical Fact Sheet

  5. Clinical Presentation • Target group: all age group • Incubation period: 24–48 hrs　潛伏期 • Presentation: Abdominal pain, diarrhea, vomiting, nausea, low-grade fever 腹痛，腹瀉，嘔吐，噁心，低燒 • Self-limiting • Complication: dehydration　脫水 Source: CDC Technical Fact Sheet

  6. Characteristics of NV infection • Diagnosis may be difficult • Unable to culture • Poor antigenic immunogenicity • Highly infectious • No vaccine available

  7. Norovirus outbreak in HK (2001-2004) Communicable Diseases Watch

  8. Current Situation 2006-4-21(頭條日報) 2006-5-1(SCMP) 2006-6-15(明報) 2006-5-2(蘋果日報)

  9. Situation in HK (Jan-May) 2006 Residential care home for the elderly Until Jun 20, 2006 74 outbreaks 999 persons affected Communicable Diseases WATCH (May 28–June 10, 2006) CHP, DH, HKSAR

  10. Why is it so infectious?How severe is NV infection in community?

  11. Design • 12-month survey of patients with acute diarrhea in PWH, both in-patients and out-patients • Dec 2004 – Nov 2005 • Stool samples were collected within 48h of symptom onset • Detection of NV by quantitative RT-PCR

  12. Results • 651 fecal specimens were collected in this 12-month study • 54 (8.3%) NoV-positive GI (8) GI/II (9) NV GII (37)

  13. Patients’ characteristics *NV GI versus GII only.

  14. Norovirus and temperature

  15. Monthly distribution of norovirus and temperature Air temperature NoV

  16. Viral load and temperature

  17. How infectious?

  18. Viral Load in Stool

  19. Viral load and genogroup GII has 100-fold higher viral load in stool than GI

  20. Conclusions • Norovirus accounts for 8% of acute sporadic diarrhea in Hong Kong • There is a close correlation between mean temperature and norovirus-associated diarrhea • Billions of norovirus can be present in the stool samples of infected individuals, particularly for GII

  21. Implications of Our Research • Rapid testing of NV should be available to more laboratories in Hong Kong • A more comprehensive surveillance program for NV is needed

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