In cases of infectious ON, incubation periods vary with the causative agent. Neonates may acquire Chlamydia trachomatis or Neisseria gonorrhoeae from their infected mothers during birth, and symptom onset typically occurs 5 to 14 days or 2 to 5 days afterwards, respectively [1]. Other infectious diseases may be contracted later on and may thus manifest in newborns aged two weeks and older. Initially, catarrhal conjunctivitis may be observed. Ocular discharge may turn mucopurulent within a few days, and additional signs like chemosis, eyelid edema, blepharitis, and keratitis may be noted. In severe cases, corneal ulcers may form and lead to blindness. The presence of respiratory symptoms may indicate the concomitant involvement of respiratory system. Affected neonates commonly present feeding difficulties.

ON due to the instillation of silver nitrate generally manifests within two days.

As it has been indicated above, distinct pathogens may account for infectious ON. It is of major importance to identify the causative pathogen in individual cases. Infections with Chlamydia trachomatis or Neisseria gonorrhoeae may cause systemic disease and life-threatening complications like pneumonia and sepsis. Although less frequently reported, complications may also arise from infections with other pathogens [7]. It is important to note that the determination of the etiological agent and its susceptibility to antimicrobials is of significant therapeutic relevance [8].

In order to prove the presence of bacterial pathogens, conjunctival swabs should be taken and samples should be prepared for Gram staining [9], bacterial culture, and molecular biological assays. Of note, Chlamydia trachomatis is an obligate intracellular microorganism and thus can not be grown on conventional media [10]. It is best detected by means of polymerase chain reaction. In contrast, Neisseria gonorrhoeae may be grown on Thayer-Martin or Martin-Lewis agar. Nevertheless, nucleic acid amplification tests may also be carried out to detect this pathogen and are increasingly replacing conventional methods.

Molecular biological assays are also indicated to prove the presence of viral pathogens.

ON may indicate an infection with either of the following bacterial pathogens [6]:

• Chlamydia trachomatis
• Neisseria gonorrhoeae
• Staphylococcus aureus
• Staphylococcus epidermidis
• Streptococcus pneumoniae
• Streptococcus viridans
• Enterobacter spp.
• Escherichia coli
• Klebsiella pneumoniae
• Proteus spp.
• Serratia marcescens
• Haemophilus influenzae
• Pseudomonas aeruginosa

Rarely, ON results from an infection with adenoviruses or herpes simplex virus [5].

Silver nitrate has been used to prevent neonatal conjunctivitis induced by Neisseria gonorrhoeae. However, this measure may provoke non-infectious, chemical conjunctivitis.

Ophthalmia neonatorum (ON), a condition also referred to as neonatal conjunctivitis, is defined as an inflammation of the mucous membranes of the eye of newborns during their first month of life. ON may be a result of bacterial or viral infection, or may be caused by the instillation of chemical agents. While many cases resolve spontaneously within a few days, severe complications may occur [1]. In fact, ON may result in blindness [2] [3]. Fortunately, ON-associated morbidity has decreased significantly since antimicrobial medications have become widely available.

Newborns may contract the respective infections during vaginal delivery or postnatally from colonized family members or healthcare professionals; chemical ON is related to the prophylaxis of infectious ON. Nevertheless, prophylactic measures are indicated in neonates born to mothers suffering from chlamydia infection or gonorrhea, and in all newborns in underdeveloped regions with high prevalence rates of these sexually transmissible diseases. No consensus has been reached regarding the application of prophylactic measures in neonates born to apparently healthy mothers in developed countries [4] [5].

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9. Alexandre I, Cortes N, Justel M, Fernandez I, Ortiz de Lejarazu R, Pastor JC. The value of simple microbiological studies for on-site screening of acute neonatal conjunctivitis in Angola. J Ophthalmic Inflamm Infect. 2014;4(1):1.
10. Centers for Disease Control and Prevention. Recommendations for the laboratory-based detection of Chlamydia trachomatis and Neisseria gonorrhoeae--2014. MMWR Recomm Rep. 2014;63(RR-02):1-19.