Table 4– Total number of children, cases of lower respiratory tract infection (LRTI) during the first 12–14 months of life and crude and adjusted relative risk (RR) for continuous exposure and for each quartile (Q) of dichlorodiphenyldichloroethylene (DDE), hexachlorobenzene (HCB) and sum of polychlorinated biphenyls (ΣPCBs) exposure within the Spanish study population

	Exposure level ng·g⁻¹ of lipid	LRTI cases n (%)	Crude RR (95% CI)	p-value	Adjusted RR^# (95% CI)	p-value	Multipollutant adjusted RR^¶ (95% CI)	p-value
DDE
Continuous		1342 (35.4)	1.04 (0.95–1.14)	0.43	1.11 (1.00–1.22)	0.05	1.11 (0.99–1.24)	0.07
Q1	<72.6	336 (32.4)	1		1		1
Q2	72.6–115.9	335 (35.5)	1.10 (0.89–1.35)	0.40	1.16 (0.94–1.43)	0.16	1.20 (0.97–1.48)	0.09
Q3	115.5–191.7	336 (39.9)	1.23 (1.00–1.51)	0.05	1.33 (1.08–1.62)	0.01	1.40 (1.13–1.73)	<0.01
Q4	>191.7	335 (33.7)	1.04 (0.84–1.29)	0.72	1.20 (0.96–1.51)	0.11	1.28 (1.00–1.64)	0.04
HCB⁺
Continuous		1341 (35.4)	1.00 (0.92–1.10)	0.87	1.06 (0.95–1.17)	0.30	1.03 (0.92–1.15)	0.63
Q1	<26.4	336 (35.4)	1		1		1
Q2	26.4–46.4	335 (34.9)	0.98 (0.80–1.21)	0.89	0.96 (0.79–1.18)	0.72	0.95 (0.78–1.17)	0.65
Q3	46.4–79.0	335 (37.0)	1.04 (0.85–1.28)	0.67	1.08 (0.88–1.32)	0.47	1.03 (0.84–1.29)	0.74
Q4	>79.0	335 (34.3)	0.97 (0.79–1.19)	0.77	1.06 (0.84–1.33)	0.63	1.03 (0.80–1.33)	0.80
ΣPCBs^§
Continuous		1339 (35.3)	0.95 (0.83–1.08)	0.44	1.00 (0.86–1.18)	0.93	0.92 (0.77–1.11)	0.39
Q1	<79.4	335 (37.9)	1		1		1
Q2	79.4–113.7	335 (36.1)	0.95 (0.78–1.16)	0.63	0.98 (0.80–1.20)	0.83	0.90 (0.73–1.11)	0.34
Q3	113.7–158.6	335 (35.5)	0.94 (0.77–1.14)	0.52	0.94 (0.75–1.17)	0.56	0.83 (0.66–1.05)	0.13
Q4	>158.6	334 (31.7)	0.84 (0.70–1.03)	0.10	0.84 (0.65–1.08)	0.17	0.73 (0.56–0.95)	0.02

^#: adjusted according to region, sex of the child, age and pre-pregnancy weight of the mother, allergic or asthmatic mother, parity (first child) and social class, predominant breastfeeding, maternal smoking status (during pregnancy and during the first year of life of the child) and daycare attendance during the first year of life; ^¶: also adjusted for DDE, HCB and ΣPCBs (n=1338); ⁺: one child was excluded from the analysis with HCB because it was an outlier (n=1341); ^§: two children had no information for PCBs within the Spanish population and one was excluded from the analysis with ΣPCBs because it was an outlier (n=1339).