glht (multicomparisons) with a binomial response variable

Hi,
I,ve a run a model like this
mcrm<-glm(catroj~month,binomial)
      being catroj a binary response variable with two levels (infected
and non infected) 

anova(mcrm3,test="Chisq")

     Df Deviance Resid. Df Resid. Dev P(>|Chi|)    
NULL                   520     149.81              
mes   3    16.86       517     132.94 0.0007551 ***

When I?m trying to do a post comparisons between factors i tried with glht
of multcomp package by Torsten Hothorn I use "Tukey" contrast, but d?dn't
get diferencies

 > summary(glht(mcrm3,linfct=mcp(month="Tukey")))

                    Estimate Std. Error z value Pr(>|z|)  
may - april == 0   -18.2470  1555.0564  -0.012   1.0000  
june - april == 0   -1.9436     0.8307  -2.340   0.0671 .
july - april == 0   -0.6253     0.5477  -1.142   0.6133  
june - may == 0    16.3034  1555.0565   0.010   1.0000  
july - may == 0    17.6216  1555.0563   0.011   1.0000  
july - june == 0    1.3182     0.7899   1.669   0.2870  

I'm afraid "Tukey" it is not the correct contrast, but, What should i use
for a binary response variable?
Any advice, please?