Comparative analysis of Streptococcus pneumoniaetransmission in Portuguese and Finnish day-care centres

BMC Infectious Diseases

Table 3 Acquisition and clearance of Streptococcus pneumoniae carriage in 3 day-care centres in Finland, 2001–2002

		Clearance		Acquisition in non-carrying children		Acquisition in carrying children
Target serotype	Exposure¹	Events	Person-time²	Events	Person-time³	Events	Person-time⁴
9V	Yes	7	12	7	56	1	14
9V	No	3	3	6	300	1	83
18C	Yes	7	16	9	87	0	11
18C	No	4	4	1	269	0	81
3	Yes	1	3	6	105	1	30
3	No	8	11	4	251	0	68
15BC	Yes	1	4	1	77	0	19
15BC	No	5	12	7	279	0	77
19A	Yes	4	5	0	35	0	8
19A	No	3	3	2	321	0	96
19F	Yes	2	3	1	28	1	8
19F	No	2	8	2	328	1	93
11A	Yes	2	2	0	18	0	8
11A	No	0	4	1	338	5	98
14	Yes	0	0	0	12	0	5
14	No	3	4	2	344	1	103
35F	Yes	0	1	1	40	0	13
35F	No	1	3	1	316	2	95
38	Yes	0	0	0	24	0	13
38	No	2	3	2	332	0	96
22	Yes	0	0	0	20	0	0
22	No	1	5	0	336	2	107
33	Yes	0	0	0	0	0	0
33	No	0	0	2	356	0	112
6A	Yes	0	0	0	8	0	6
6A	No	1	1	1	348	0	105
6B	Yes	0	0	0	12	0	7
6B	No	1	2	1	344	0	103
7	Yes	0	0	0	9	0	1
7	No	1	1	1	347	0	110
10	Yes	0	0	0	4	0	2
10	No	1	1	0	352	0	109
18B	Yes	0	0	0	3	0	1
18B	No	1	1	0	353	0	110
35B	Yes	0	0	0	0	0	0
35B	No	0	0	1	356	0	112
9N	Yes	0	0	0	0	0	0
9N	No	0	0	1	356	0	112
16⁵	Yes	0	0	0	7	0	4
16⁵	No	0	0	0	349	0	108
Total:	Yes	24	46	25	545	3	150
	No	37	66	35	6575	12	1978
	No	61	112	60	7120	15	2128

The crude estimates of the model parameters are (cf. Appendix): the transmission rate $\hat{β} = (25 - \hat{κ} \times 545) / 85.26 = 0.26$ (per month); the community acquisition rate per serotype (in non-carrying children) $\hat{κ} = 35 / 6575 = 0.005$ (per month); the clearance rate of carriage $\hat{μ} = 61 / 112 = 0.54$ (per month); the competition parameter $\hat{φ} = (12 / 1978) / (35 / 6575) = 1.14$ . For parameter β, the denominator (85.26) is not directly readable from the data as presented in the table. Only samples from two consecutive visits were considered (85% of the scheduled pairs of consecutive visits).
¹ Exposure is here defined as the presence of at least one carrier of the target serotype in the other attendees in the room.
² Person-time here is the total time, in months, spent carrying pneumococcus overall (total row) or a specific serotype (serotype rows) stratified by the presence or absence of other carriers of the specific serotype.
³ Person-time here is the total time, in months, spent as a non-carrier, stratified by exposure to the specific serotype. For the total row, the time is a sum of serotype-specific person-times.
⁴ As in ² but for children carrying pneumococcus.
⁵ Sampled only once in a child which was missing at the next visit.

ISSN: 1471-2334