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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)
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