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Table 5 Probability that anecdotally-linked outbreaks have a common source based on epidemiological and virological sequence data sequence.

From: Linking healthcare associated norovirus outbreaks: a molecular epidemiologic method for investigating transmission

Pair

Variantx

Varianty

Δ (bases)

Description of epidemiological link

a

b

Probability of transmission link

1

1A

1A

0

Doctor exposed on affected ward then worked on another ward while ill. Outbreak began on this ward 1 day later.

1.0

0.38 (23/60)

72%

2

3D

3E

3*

Transfer from nursing home into hospital (ward unspecified)

0.004

0.016 (1/60)

20%

3

1H

2M

4**

Transfer from hospital to nursing home of primary case

0.001

0.016 (1/60)

6%

4

1A

1A

0

Transfer from hospital to nursing home

1.0

0.38 (23/60)

72%

5

1A

1A

0

Transfer of patient from hospital affected to unaffected wards

1.0

0.38 (23/60)

72%

  1. a Probability that the viruses could be drawn from the same outbreak basic on genetic similarity
  2. b Probability that second virus would randomly be drawn from the viral population
  3. c Probability that outbreaks with anecdotal links had a transmission link: P(x|Type = M) = ca/(ca+(1-c)b)
  4. *3 nucleotide differences in the capsid
  5. ** 1 nucleotide difference in polymerase, 3 nucleotide differences in the capsid