WordWeb Online

1. Contaminated with infecting organisms
   "pestiferous wounds"
   - dirty
    
2. Likely to spread and cause an epidemic disease
   - pestilent, pestilential, plaguey
    
3. Tending to corrupt or pervert
   - corruptive, perversive
    
4. Causing irritation or annoyance
   - annoying, bothersome, galling, irritating, nettlesome, pesky, pestering, plaguy, plaguey, teasing, vexatious, vexing

See also: disagreeable, epidemic, evil, infected, septic