Investigation of possibility of human to human transmission Bureau - - PowerPoint PPT Presentation

Investigation of possibility of human to human transmission

Bureau of Epidemiology Wanna Hanshaoworakul

WHY? cluster investigation

Mathematic model for H5N1 transmission without control measure in Thailand

1 2

60 days 30 days

3

90 days

4

120 days

5

150 days

6

180 days

Infected not transmit Infected and transmit

After infection

Effect of intervention in containing

• utbreak at the source

• Antiviral prophylaxis can contain the epidemic

when

R0 < 1.6

Intervention have to start within 21 days after onset of the first case

• Other intervention such as isolation, limit the

travel will accelerate the success

Model summary

Signal for phase Signal for phase 4 4

• Epidemiological signal
• Virological signal
• cluster of five closely related cases

(including the index case) in which H-H transmission is suspected

• Pneumonia of 3 cases in the same

place or join same activities and at least one has severe respiratory symptom

• Detection of a virus with new genetic

and antigenic feature

• Isolation of a virus from a human case

showing a number of mutations not seen in avian isolates

Source:WHO pandemic influenza draft protocol for rapid response and contatinment

Evidence of mammal to mammal transmission

Experimental demonstrate cat to cat H5N1 transmission These results show that domestic CATs are at risk of disease or death from H5N1 virus, can be infected by horizontal transmission, and may play a role in the epidemiology of this virus

Tiger zoo

• utbreak
• A tiger zoo in Sriracha, Chonburi, Thailand, was affected by

HPAI beginning on October 11, 2004.

• On October 16, 2004, the tigers were fed cooked chicken

carcasses or pork.

• Four weeks after the last tiger was infected, 58 serum from all

humans contacted with either the animals or their tissue or fluid. Seroconversion (1:80, ≥1:640) occurred 6 weeks after the incident in only 2 (3.5%) persons who had shown no clinical signs of illness.

Source: EID: Volume 11, Number 5—May 2005

Evidence of Human to Human transmission

Transmission of H5N1 in serological study Transmission of H5N1 in serological study

Transmission from patient to HCW

Cluster investigation

Onset Day 2 6 10 12 14 18 Exposure 4 8 16

Median of day

Clinical progression

ARDS

24-01-04 26-01-04

Pneumonia

21-01-04

date

Timeline of Avian Influenza Case

30 2 4 6 8 10 12 14 16 18 20 22

Chicken died about 10 chicken/day in Yeao’s House People reported Collected specimen testing Culling poultry in Moo 9 H5N1 poultry report Prepared & Cooked & Ate sick chicken Onset Date OPD R/o TB IPD R/o AI Death Prepared & Ate sick chicken Onset Date Admit

Moo 9, Pang-tru subdistrict, Panom Thuan district, Kanchanaburi province

Thai boy 7 yr, Ronarit Thai man 48 yr, Bangorn Poultry situation

Started oseltamivir

Excluded H-H

• Onset of both cases unlikely to be H-H
• The second case also expose to environment of

dead poultry

Probable human to human transmission

Possible H-H

• Onset of the second case 2 days after contact to the index

case

• The second case had no exposure to poultry
• The aunt might expose to contaminated environment, or

taking care of the index case. Possible to get infection from either sources but unlikely to get infection from mother

• The virus from this cluster showed no adaptive change in the

receptor-binding site from the avian 2,3-linked pattern toward the 2,6-linked pattern of the human sialic acid receptor.

Cluster in North Sumatra

All confirmed cases in the cluster can be directly linked to close and prolonged exposure to a patient during a phase of severe illness. Although human- to-human transmission cannot be ruled out, the search for a possible alternative source of exposure is continuing.

Analysis of viruses

• Full genetic sequencing of two viruses isolated from cases in

this cluster has been completed by WHO H5 reference laboratories in Hong Kong and the USA. Sequencing of all eight gene segments found no evidence of genetic reassortment with human or pig influenza viruses and no evidence of significant mutations.

• The viruses showed no mutations associated with resistance to

the neuraminidase inhibitors, including oseltamivir (Tamiflu).

• The human viruses from this cluster are genetically similar to

viruses isolated from poultry in North Sumatra during a previous

• utbreak.

Consideration of Human to Human

• Duration between onsets of index case

and secondary cases

• Infectious sources: poultry, or environment

can be excluded?

• Risk of transmission: duration of exposed,

high viral load, intimate contact

Questions for cluster investigation

• Confirmation of infection
• Sharing same exposure VS

H-H transmission

• Severity of the secondary case
• Mechanism of transmission
• Extent of transmission
• Possibility of containment

Lab contamination

Contaminated environment excluded Public health important

• f mild disease

droplet, aerosol, fomite number of secondary cases International assistances

Suggested activities

• Qualified specimens taken from all contact

– Household – Health care workers – Social closed contact

• Closed monitoring all contacts for anti-viral

compliance and fever

• Active case finding in affected areas
• Timely intervene of containment measures
• Assess effectiveness of control measure
• Adjusted national strategic plan (phase4 or 5)

– Contain outbreak VS Prevent mortality

Thank you Thank you

Ｄｒ Ｋｕｍｎｕａｎ Ｕｎｇｃｈｕｓａｋ Ｄｒ Ｄａｒｉｎ Ａｒｅｅｃｈｏｋｅｃｈａｉ ＷＨＯ Ｇｅｎｅｖａ