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Table 4 The effect of exposure on the rate of pneumococcal acquisition in day care attendees.

From: Clustering of serotypes in a longitudinal study of Streptococcus pneumoniae carriage in three day care centres

Exposure stratum

Person-months* in children at risk of acquisition

Number of acquisitions

Rate of acquisition per month per 100 children (90% confidence interval)

None

7732

35

0.45 (0.34 – 0.60)

DCC only

1074

27

2.51 (1.83 – 3.45)

Family and

64

8

12.50 (7.00–22.32)

DCC

   

Family only

22

1

4.55 (0.88–23.43)

Total

8892

71

0.80 (0.66 – 0.97)

  1. Acquisition rates were determined in the following exposure strata: no observed carriage, carriage in the day care centre (DCC) only, carriage in both and carriage in the family only. The acquisition rates were calculated from the number of acquisitions for children at risk, i.e., not carrying the target type at the previous visit. The same acquisition rate was assumed for all serotypes.
  2. * person-months were calculated from the number of children at risk at the start of the one-month observation interval, each contributing one month of person-time