<prompt> Which of the following is the likely organism causing ophthalmia neonatorum on the 3rd day of bih?N gonorrhoeaeChlamydiaStreptococcusHaemophilus influenzae  <response>: The common causative organisms of ophthalmia neonatorum include Chlamydia trachomatis most common, Neisseria gonorrhoeae most threatening, Haemophilus species, Streptococcus species, Staphylococcus aureus, and viruses such as Herpes simplex HSV. The rule of fives is a mnemonic for predicting the most likely bacterial etiology of the condition. However, there is considerable overlap in times to onset. 0 to 5 days: N gonorrhoeae 5 days to 5 weeks: Chlamydia 5 weeks to 5 years: Streptococcus or Haemophilus influenzae Ref: Levsky M.E., DeFlorio P. 2010. Chapter 2. Ophthalmologic Conditions. In K.J. Knoop, L.B. Stack, A.B. Storrow, R.J. Thurman Eds, The Atlas of Emergency Medicine, 3e. 