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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