The Collaborative International Dictionary of English v.0.48:

Infectious disease \In*fec"tious dis*ease"\
      (a) Any disease caused by the entrance, growth, and
          multiplication of microorganisms in the body; a germ
          disease. It may not be contagious.
      (b) Sometimes, as distinguished from contagious disease,
          such a disease communicated by germs carried in the
          air or water, and thus spread without contact with the
          patient, as measles.
          [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

infectious disease
    n 1: a disease transmitted only by a specific kind of contact

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "infectious disease":
   abnormality, acute disease, affection, affliction, ailment,
   allergic disease, allergy, atrophy, bacterial disease,
   birth defect, blight, cardiovascular disease, chronic disease,
   circulatory disease, complaint, complication, condition,
   congenital defect, defect, deficiency disease, deformity,
   degenerative disease, disability, disease, disorder, distemper,
   endemic, endemic disease, endocrine disease, epidemic disease,
   functional disease, fungus disease, gastrointestinal disease,
   genetic disease, handicap, hereditary disease, iatrogenic disease,
   illness, indisposition, infirmity, malady, malaise, morbidity,
   morbus, muscular disease, neurological disease,
   nutritional disease, occupational disease, organic disease,
   pandemic disease, pathological condition, pathology, plant disease,
   protozoan disease, psychosomatic disease, respiratory disease,
   rockiness, secondary disease, seediness, sickishness, sickness,
   signs, symptomatology, symptomology, symptoms, syndrome, the pip,
   urogenital disease, virus disease, wasting disease, worm disease