. 2021 May 3;16(5):e0250871. doi: 10.1371/journal.pone.0250871

Table 3. Determinants of an incident chlamydia, gonorrhoea, and chlamydia and/or gonorrhoea infection, EVRI study, Cape Town, South Africa, October 2012-February 2014.

	Incident chlamydia (n = 48)^a						Incident gonorrhoea (n = 29)^b						Incident chlamydia and/or gonorrhoea (n = 70)^c
	IRR	(95% CI)	p	aIRR^d	(95% CI)	p	IRR	(95% CI)	p	aIRR^e	(95% CI)	p	IRR	(95% CI)	p	aIRR^f	(95% CI)	p
1. Socio-demographic characteristics
Age, continuous^g	0.77	(0.19;3.07)	0.71	2.92	(0.53;16.1)	0.22	0.79	(0.13;4.76)	0.80	0.76	(0.09;6.37)	0.80	0.69	(0.21;2.19)	0.52	1.34	(0.33;5.39)	0.68
Age, categorical
< 20 year	REF		0.76				REF		0.65				REF		0.66
20–21 year	0.97	(0.50;1.89)					1.24	(0.54;2.87)					0.92	(0.53;1.59)
≥ 22 year	0.78	(0.39;1.57)					0.80	(0.31;2.06)					0.76	(0.43;1.37)
Race
Black	REF		0.22				REF		0.75				REF		0.68
Other	0.35	(0.05;2.54)					1.27	(0.30;5.37)					0.79	(0.25;2.53)
Highest education level
≤ Grade 12	REF		0.77				REF		0.047				REF		0.10
Passed grade 12	0.86	(0.40;1.86)					0.37	(0.11;1.27)					0.63	(0.32;1.24)
Some college/tech	0.75	(0.34;1.68)					0.26	(0.06;1.14)					0.49	(0.23;1.05)
Marital status
Single	REF		0.33				^h						REF		0.21
Other	0.42	(0.06;3.08)											0.35	(0.05;2.51)
Alcohol use in past month
No	REF		0.85				REF		0.06				REF		0.36
Yes	0.94	(0.50;1.76)					2.45	(0.90;6.63)					1.28	(0.74;2.21)
Current smoker
No	REF		0.03	ⁱ			REF		0.31				REF		0.58
Yes	0.18	(0.03;1.34)					1.82	(0.62;5.37)					0.78	(0.31;1.95)
2. Sex related characteristics
Age at first sex act, continuous^g	1.87	(0.24;14.46)	0.55				0.58	(0.04;8.92)	0.70				1.00	(0.17;5.76)	1.00
Age at first sex act, categorical
< 16 year	REF		0.73	REF			REF		0.32	REF			REF		0.31	REF
16–17 year	1.59	(0.59;4.26)		1.17	(0.42;3.24)	0.77	1.90	(0.54;6.68)		1.67	(0.46;6.10)	0.44	1.80	(0.79;4.10)		1.57	(0.67;3.68)	0.29
≥ 18 year	1.67	(0.58;4.81)		1.00	(0.32;3.10)	1.00	0.95	(0.21;4.24)		0.71	(0.11;4.43)	0.71	1.28	(0.51;3.21)		1.05	(0.39;2.85)	0.92
Ever been pregnant
No	REF		0.64				REF		0.35				REF		0.28
Yes	1.15	(0.64;2.08)					1.42	(0.67;3.01)					1.31	(0.80;2.14)
Current birth control use
No	REF		0.63				REF		0.18				REF		0.36
Yes	1.17	(0.61;2.27)					1.90	(0.70;5.16)					1.30	(0.74;2.29)
Type of birth control
No current use	REF		0.62				REF		0.07				REF		0.58
Condom	1.40	(0.69;2.83)					1.30	(0.41;4.10)					1.30	(0.70;2.42)
Depo-Provera	0.99	(0.40;2.49)					2.18	(0.66;7.13)					1.17	(0.55;2.50)
Oral contraceptives	0.44	(0.06;3.38)					3.90	(0.93;16.30)					1.42	(0.48;4.23)
Lifetime number of sex partners, continuous^j	1.12	(0.67;1.84)	0.67				1.45	(0.78;2.70)	0.26				1.24	(0.82;1.87)	0.31
Lifetime number of sex partners, categorical
< 3	REF		0.35	REF			REF		0.002	REF			REF		0.08	REF
3–4	1.52	(0.77;3.01)		1.47	(0.74;2.95)	0.27	6.72	(1.92;23.59)		7.29	(2.05;26.00)	0.002	1.95	(1.08;3.55)		1.93	(1.06;3.53)	0.03
≥ 5	0.86	(0.36;2.08)		0.76	(0.29;1.98)	0.58	4.52	(1.13;18.07)		4.32	(1.07;17.46)	0.040	1.48	(0.73;3.00)		1.36	(0.65;2.84)	0.42
Sex partners since start study, continuous^j	0.91	(0.50;1.66)	0.75				0.95	(0.40;2.22)	0.90				0.91	(0.53;1.56)	0.74
Sex partners since start study, categorical
0	REF		0.16				REF		0.87				REF		0.19
1	2.50	(0.76;8.25)					1.41	(0.32;6.31)					2.19	(0.78;6.15)
≥ 2	1.59	(0.44;5.69)					1.48	(0.31;6.98)					1.56	(0.52;4.67)
Condom use since start study
No sex	REF		0.57				REF		0.30				REF		0.33
Always	1.98	(0.59;6.64)					1.11	(0.24;5.12)					1.77	(0.62;5.06)
More than half of the time	1.77	(0.40;7.89)					1.08	(0.15;7.69)					1.67	(0.47;5.91)
Half of the time	2.44	(0.58;10.21)					1.13	(0.16;8.02)					1.75	(0.49;6.21)
Less than half of the time or never	2.89	(0.75;11.16)					3.26	(0.68;15.71)					3.01	(0.98;9.23)
Sex for presents/money/drugs for sex since start study
No	REF		0.74				REF		0.41				REF		0.47
Yes	1.29	(0.31;5.34)					1.94	(0.45;8.31)					1.49	(0.54;4.12)
Prevalent infection at baseline^k
No	REF			REF			REF						REF			REF
Yes	4.14	(2.33–7.35)	<0.001	5.83	(3.01;11.28)	<0.001	1.66	(0.40;7.00)	0.52				2.23	(1.38;3.58)	0.001	2.54	(1.47;4.38)	0.001

Abbreviations: aIRR, adjusted incidence ratio; CI, confidence interval; IRR, incidence rate ratio; REF, reference category

^a. 9 incident events were excluded from multivariable analysis due to missing values

^b. 7 incident events were excluded from multivariable analysis due to missing values

^c. 14 incident events were excluded from multivariable analysis due to missing values

^d. Variables included in the multivariable model based on univariable analysis: age, lifetime number of sex partners, age at first sex act, prevalent chlamydia infection at baseline

^e. Variables included in the multivariable model based on univariable analysis: age, lifetime number of sex partners, age at first sex act

^f. Variables included in the multivariable mode based on univariable analysis: age, lifetime number of sex partners, age at first sex act, prevalent chlamydia and/or gonorrhoea infection at baseline

^g. Per 10 year increase in age

^h. Excluded from univariable and multivariable analysis due to 0 observations in one of the categories

ⁱ. Excluded from multivariable analysis due to being unstable in the model (large standard error and 95% confidence interval)

^j. Per (log+1) increase in partner

^k. Chlamydia, gonorrhoea, or chlamydia and/or gonorrhoea, respectively.