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Table 4 Factors associated with finding a malaria infection during investigation of an incident malaria case in Southern Province, Zambia

From: Location, location, location: environmental factors better predict malaria-positive individuals during reactive case detection than index case demographics in Southern Province, Zambia

Measure Categorization Unadjusted IRR (95% CI) Adjusted IRR (95% CI)
Topographical position index 270 m Flat Reference Reference
Valley 1.115 (0.916–1.442) 1.019 (0.733–1.417)
Ridge 1.268* (1.034–1.554) 1.590* (1.106–2.286)
Lower slope 0.994 (0.780–1.268) 1.211 (0.893–1.645)
Upper slope 1.872*** (1.496–2.341) 1.979*** (1.521–2.573)
Topographical position index 4950 m Flat Reference Reference
Valley 1.000 (0.817–1.224) 1.032 (0.780–1.365)
Ridge 0.962 (0.782–1.183) 0.576** (0.419–0.792)
Lower slope 0.732** (0.583–0.919) 0.654** (0.491–0.871)
Upper slope 1.398** (1.152–1.696) 1.153 (0.909–1.462)
Enhanced vegetation index lagged 4 weeks <0.5 Reference Reference
≥0.5 1.668** (1.209–2.328) 1.291 (0.894–1.865)
Median enhanced vegetation index <0.25 Reference Reference
≥0.25 1.740*** (1.512–2.002) 1.259* (1.049–1.513)
Altitude ≤1100 m Reference Reference
>1100 m 1.442*** (1.252–1.661) 0.949 (0.783–1.151)
Wetness index ≤10.2 (drier) Reference Reference
>10.2 (wetter) 1.061 (0.918–1.225) 1.432*** (1.198–1.712)
Convergence index ≤0 (wetter) Reference Reference
>0 (drier) 1.030 (0.897–1.184) 0.811* (0.665–0.989)
Index case travelled No travel in previous 2 weeks Reference Reference
Travel in previous 2 weeks 0.898 (0.789–1.188) 0.776 (0.544–1.106)
Timeliness of case investigation Same week as incident case Reference Reference
At least 1 week following incident case 1.381* (1.072–1.780) 1.211 (0.905–1.621)
Gender of index case Female Reference Reference
Male 1.329** (1.132–1.560) 0.943 (0.765–1.162)
Travel among individuals in community tested No travel in previous 2 weeks Reference Reference
Any travel in previous 2 weeks 0.670*** (0.587–0.766) 0.805* (0.668–0.969)
Age of index case >15 years old Reference Reference
5–15 years old 0.898 (0.740–1.091) 0.862 (0.685–1.085)
<5 years old 0.761 (0.565–1.025) 0.686* (0.484–0.973)
  1. Zero-inflated Poisson regression models were inflated by the number of people tested and month of the year. Models also controlled for seasonality with a sinusoidal function
  2. N = 690 case investigations
  3. CI confidence interval, IRR incident rate ratio
  4. *p < 0.05 **p < 0.01 ***p < 0.001