Table 2.

Risk factor analysis of multiple episodes of malaria in western Thailand

Characteristics	Total	Not infected	Single episode	Multiple episodes	Odds ratioa (95% CI)
	N	n (%)	n (%)	n (%)
Sex
Female	3908	3739 (95.7)	145 (3.7)	24 (0.6)	1
Male	3904	3663 (93.8)	198 (5.1)	43 (1.1)	1.46 (1.19–1.78)
Age groups
< 5	1755	1657 (94.4)	82 (4.7)	16 (0.9)	1
6–10	1051	953 (90.7)	80 (7.6)	18 (1.7)	1.74 (1.30–2.33)
11–20	1705	1610 (94.4)	79 (4.7)	16 (0.9)	1.00 (0.75–1.33)
21–60	2963	2849 (96.1)	97 (3.3)	17 (0.6)	0.68 (0.51–0.89)
> 60	328	323 (98.5)	5 (1.5)	0 (0.0)	0.26 (0.11–0.65)
Ethnic groups
Thai	1083	1034 (95.5)	47 (4.3)	2 (0.2)	1
Karen	5703	5355 (93.9)	284 (5.0)	64 (1.1)	1.38 (1.02–1.88)
Other	51	50 (98.0)	1 (2.0)	0 (0.0)	0.42 (0.06–3.13)
Education attainment
Illiterate	4280	4035 (94.3)	205 (4.8)	40 (0.9)	1
Primary	1700	1580 (92.9)	98 (5.8)	22 (1.3)	1.25 (0.99–1.57)
Secondary	824	793 (96.2)	28 (3.4)	3 (0.4)	0.64 (0.44–0.94)
College	19	18 (94.7)	0 (0.0)	1 (5.3)	0.96 (0.13–7.23)
Occupational risk
Low risk work	742	728 (98.1)	13 (1.8)	1 (0.1)	1
Child/student	3632	3376 (92.9)	210 (5.8)	46 (1.3)	3.95 (2.30–6.81)
Factory laborers	393	367 (93.4)	21 (5.3)	5 (1.3)	3.70 (1.91–7.16)
Plantation workers	1187	1143 (96.3)	38 (3.2)	6 (0.5)	2.00 (1.09–3.68)
High risk work	55	53 (96.4)	2 (3.6)	0 (0.0)	1.95 (0.43–8.82)
Unspecified	820	765 (93.2)	47 (5.8)	8 (1.0)	3.74 (2.06–6.78)
Having other infected person in the same HHb
No	333	–	290 (87.1)	43 (12.9)	1
Yes	77	–	53 (66.8)	24 (31.2)	3.05 (1.71–5.45)

^aOdds ratios were based on proportional ordinal logistic model

^bOdds ratio was based on binary logistic model (comparing only infected cases)