Approach Considerations
Laboratory studies for neonatal conjunctivitis should include the following:
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Conjunctival scraping for Gram stain or Giemsa stain
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Conjunctival scraping for polymerase chain reaction assay (PCR) to detect chlamydia and gonorrhea
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Culture on chocolate agar and/or Thayer-Martin for N gonorrhoeae
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Culture on blood agar for other bacteria
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Culture of corneal epithelial cells for HSV if cornea is involved; PCR should also be considered in cases of possible HSV conjunctivitis
Culture and Histology
Bacterial cultures on blood and chocolate agar are indicated in every case of neonatal conjunctivitis and remain the criterion standard despite newer diagnostic methods.
Since Chlamydia bacteria are obligate intracellular organisms, the culture specimens need to contain epithelial cells and not just exudative material. PCR is generally accepted as the most useful test for chlamydial conjunctivitis owing to its high sensitivity. [11]
In cases in which gonorrhea is suspected, the agar should be inoculated immediately since Ngonorrhoeae is very sensitive to moisture and temperature changes.
Laboratory evaluation for the presence of HSV infection is indicated if a corneal epithelial defect is present, if vesicles are present on the eyelids or other parts of the body, and if the diagnosis cannot be made on ocular examination. The presence of HSV in tissue culture remains the criterion standard in the diagnosis of HSV, despite a high false-negative rate. HSV infections may be more rapidly diagnosed with PCR, and PCR testing for HSV is more sensitive than viral culture. [11] Laboratory evaluation for suspected HSV becomes more important in neonatal disease because the clinical presentation may be highly atypical in an immunologically immature newborn.
Cytologic findings for various forms of conjunctivitis are as follows:
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Chemical conjunctivitis - Neutrophils, occasional lymphocytes on Gram stain
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Bacterial conjunctivitis - Bacteria, neutrophils on Gram stain
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Gonococcal conjunctivitis - Neutrophils, Gram-negative intracellular diplococci on Gram stain
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Chlamydial conjunctivitis - Neutrophils, lymphocytes, plasma cells on Gram stain; basophilic intracytoplasmic inclusions in epithelial cells on Giemsa stain
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Herpetic conjunctivitis - Lymphocytes, plasma cells, multinucleate giant cells on Gram stain; eosinophilic intranuclear inclusions in epithelial cells on Papanicolaou smear, but with low sensitivity
Newer Diagnostic Techniques
Nucleic acid amplification tests such as polymerase chain reaction (PCR) and transcription-mediated amplification (TMA) are more sensitive than culture in detecting chlamydial and gonorrheal organisms. [8, 3]
PCR assays may have a higher sensitivity and similar specificity in diagnosing neonatal chlamydial conjunctivitis, compared with conventional methods. [12]
PCR for HSV from conjunctival scrapings has high sensitivity and specificity, but it is expensive, not always readily available, and is usually reserved for the diagnosis of encephalitis. Direct florescent antibody (DFA) studies are useful for rapid detection, have high sensitivity and specificity, and can be used to type the virus. [7]
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Severe purulent discharge and eyelid edema in a newborn with gonococcal conjunctivitis (confirmed with Gram stain and culture).
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Cloudy cornea without ulcer in neonatal gonococcal conjunctivitis.
