Table 3. Baseline risk factors for re-presenting with P. vivax malaria after initial P. vivax malaria.
| Cumulative risk of re-presentation with vivax malaria | Univariable analysis | Multivariable analysisb | |||
|---|---|---|---|---|---|
| Crude HR [95% CI] | p | AHR [95% CI] | p | ||
| Initial Speciesa | |||||
| Pure P. vivax | 33.8% [95%CI 33.1%–34.5%] | Reference | Reference | ||
| Mixed P. vivax/P. falciparum | 29.2% [95%CI 28.1%–30.4%] | 0.83 [0.79–0.88] | <0.001 | 0.86 [0.83–0.88] | <0.001 |
| Gendera | |||||
| Female | 33.4% [95%CI 32.5%–34.3%] | Reference | Reference | ||
| Male | 31.8% [95%CI 31.0%–32.7%] | 0.95 [0.90–0.99] | 0.019 | 1·00 [0.97–1.03] | 0.932 |
| Agea,c | |||||
| 1 to <5 yr | 49.6% [95%CI 48.4%–50.9%] | 2.54 [2.41–2.67] | <0.001 | 2.23 [2.15–2.31] | <0.001 |
| 5 to <15 yr | 31.2% [95%CI 29.7%–32.7%] | 1.35 [1.27–1.45] | <0.001 | 1.20 [1.15–1.26] | <0.001 |
| ≥15 yr | 24.2% [95%CI 23.4%–24.9%] | Reference | Reference | ||
| Yeara | |||||
| 2006 | 27.0% [95%CI 25.2%–28.8%] | 0.85 [0.77–0.94] | 0.002 | 0.85 [0.79–0.92] | <0.001 |
| 2007 | 32.4% [95%CI 30.6%–34.3%] | 1.07 [0·98–1.18] | 0.140 | 1.00 [0.93–1.07] | 0.924 |
| 2008 | 31.2% [95%CI 29.3%–33.1%] | 1.02 [0·92–1.12] | 0.757 | 1.00 [0.94–1.06] | 0.911 |
| 2009 | 35.8% [95%CI 34.0%–37.6%] | 1.21 [1.11–1.33] | <0.001 | 1.13 [1.07–1.20] | <0.001 |
| 2010 | 30.6% [95%CI 29.0%–32.3%] | Reference | Reference | ||
| 2011 | 31.9% [95%CI 30.3%–33.5%] | 1.05 [0.96–1.15] | 0.248 | 1.04 [0.99–1.10] | 0.143 |
| 2012 | 35.7% [95%CI 34.2%–37.3%] | 1.20 [1.10–1.31] | <0.001 | 1.19 [1.13–1.26] | <0.001 |
| 2013 | 33.5% [95%CI 31.4%–35.7%] | 1.18 [1.07–1.30] | 0.001 | 1.21 [1.14–1.28] | <0.001 |
| Admission Statusa | |||||
| Outpatient | 33.5% [95%CI 32.9%–34.2%] | Reference | Reference | ||
| Inpatient | 23.9% [95%CI 22.2%–25.8%] | 0.68 [0.62–0.74] | <0.001 | 0.81 [0.76–0.86] | <0.001 |
| Presentation Number | |||||
| 1 | 32.6% [95%CI 32.0%–33.2%] | Reference | Reference | ||
| 2 | 44.1% [95%CI 43.2%–45.0%] | 1.46 [1.41–1.51] | <0.001 | 1.35 [1.30–1.40] | <0.001 |
| 3 | 50.7% [95%CI 49.5%–51.8%] | 1.74 [1.68–1.81] | <0.001 | 1.54 [1.48–1.61] | <0.001 |
| 4 | 53.3% [95%CI 51.9%–54.7%] | 1.87 [1.79–1.95] | <0.001 | 1.63 [1.56–1.71] | <0.001 |
| 5 | 57.8% [95%CI 56.1%–59.5%] | 2.06 [1.96–2.16] | <0.001 | 1.79 [1.71–1.89] | <0.001 |
Note: Patients treated with blood schizontocides other than dihydroartemisinin-piperaquine, pregnant women, and infants less than 1 year of age were excluded from all the models. Abbreviations: AHR, Adjusted Hazard Ratio; CI, Confidence Interval; HR, Hazard ratio
a Univariable risks were derived from the first presentation with vivax malaria since subsequent presentations were not independent.
b Cox model stratified by ethnicity (non-Papuan, Highland Papuan, and Lowland Papuan) and primaquine treatment regimen. Other co-variables: admission status (outpatient or inpatient), age group, gender, and presentation number. The variance–covariance matrices were corrected for intraindividual correlation using robust standard errors.
c The median time to re-presenting with a vivax infection was 2.8 months for children less than 5 years of age compared with 3.4 months for 5 to <15 and 15 plus years.