TABLE 2.

Variables significantly associated with infestation of birds with larval and nymphal Ixodes ricinus ticks (in the most parsimonious negative binomial regression models) and with infection with B. burgdorferi sensu lato and its genospecies in larvae and nymphs collected from the birds (in the most parsimonious logistic regression models)a

Outcome, explanatory variable, and factorCoefficient SEOR (95% CI)Wald zP
Infestation with nymphal I. ricinus
    Mo
        July−1.60 (0.46)−3.48<0.001
        October−1.90 (0.50)−3.79<0.001
        Otherb
    Bird species/species group
        Blackbird2.80 (0.43)6.57<0.001
        Song thrush2.56 (0.43)5.90<0.001
        Finches and weaver finches0.99 (0.27)3.64<0.001
        Otherb
    Constant−0.08 (0.37)−0.21
Infestation with larval I. ricinus
    Mo
        May1.97 (0.84)2.34<0.05
        June2.37 (0.97)2.44<0.05
        July1.91 (0.84)2.28<0.05
        September3.74 (1.14)3.26<0.05
    Bird species/species group
        Song thrush3.32 (0.68)4.88<0.001
        Blackbird3.17 (0.71)4.46<0.001
        Wheatears (robin and nightingale)2.33 (0.46)5.00<0.001
        Finches and weaver finches2.14 (0.43)4.92<0.001
        Tits1.20 (0.45)2.68<0.01
        Otherb
    Constant−3.26 (0.86)−3.79
Infection of larvae with B. burgdorferi sensu lato
    Bird species/species group
        Blackbird and song thrush1.495 (81-27 × 103)4.93<0.001
        Otherb
    Constant0.002 (0-0.01)−5.96
Infection of nymphs with B. burgdorferi sensu lato
    Mo
        May to July32.46 (3.03-343.77)2.88<0.01
        Otherb
    Constant0.004 (0-0.05)−4.34
Infection of larvae with B. garinii
    Yr
        200122.42 (1.16-103.01)−2.06<0.05
        2002b
    Bird species/species group
        Blackbird and song thrush4.817 (44-44 × 104)3.54<0.001
        Otherb
    Constant0.004 (0-0.15)−3.02
Infection of nymphs with B. garinii
    Bird species/species group
        Blackbird and song thrush28.79 (4.35-190.57)3.49<0.001
        Otherb
    Constant0 (0-0.01)−4.56
Infection of nymphs with B. valaisiana
    Bird species/species group
        Blackbird and song thrush7.48 (2.08-26.84)3.09<0.01
        Otherb
    Constant0.03 (0.01-0.08)−6.55
  • a For both negative binomial and logistic regression models, the most parsimonious models were those in which no explanatory variables could be removed without significantly (P < 0.05) affecting model deviance. OR, odds ratio; 95% CI, 95% confidence interval.

  • b Reference factor.