( Contact ( ( spread ( by ( pathogens ( that ( are ( present ( in secretions ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Contact)) (VP (VBD spread) (PP (IN by) (NP (NP (NNS pathogens)) (SBAR (WHNP (WDT that)) (S (VP (VBP are) (ADJP (JJ present) (PP (IN in) (NP (NNS secretions)))))))))) (. .)))
Contact spread by pathogens that are present in secretions.
(ROOT (S (NP (NP (JJ Pathogens) (NN spread)) (PRN (-LRB- -LRB-) (PRP s) (-RRB- -RRB-))) (VP (VBZ stis) (PP (IN during) (NP (JJ sexual) (NN contact)))) (. .)))