How is lice presence determined? - briefly
Lice infestation is confirmed by a thorough visual examination of the scalp and hair, using a fine‑tooth comb to detect live insects and attached nits, often supplemented by microscopic analysis if needed.
How is lice presence determined? - in detail
Detection of a lice infestation begins with a systematic visual examination of the scalp and hair. Inspectors separate hair strands with a fine-toothed comb, ideally a lice comb with teeth spaced 0.2 mm apart, and observe the comb’s contents after each pass. Live insects, nymphs, or viable eggs (nits) attached to the comb indicate an active problem.
Key procedures include:
- Direct visual inspection: Examine the scalp under adequate lighting, focusing on the nape, behind the ears, and the crown. Look for adult lice (approximately 2–4 mm, grayish‑brown) and their translucent eggs cemented to hair shafts.
- Wet‑comb method: Apply a drop of water or a light conditioner to the hair, then comb through with a lice‑specific comb. The moisture slows the insects, making them easier to capture and identify.
- Microscopic confirmation: Collect suspected nits and place them on a microscope slide. Viable nits exhibit a clear embryonic development; empty shells appear white or opaque.
- Adhesive tape test: Press clear adhesive tape onto the scalp, then examine the tape under magnification for attached lice or eggs. This technique is useful for infants or individuals with dense hair where combing is difficult.
- Molecular diagnostics: In research or outbreak investigations, polymerase chain reaction (PCR) assays can detect lice DNA from hair or scalp swabs, providing definitive identification when visual methods are inconclusive.
Interpretation of findings follows a clear hierarchy. The presence of live adults or mobile nymphs confirms an active infestation. Detection of viable nits without adults suggests a recent or ongoing problem, while empty nits alone may indicate a past infestation but do not require treatment.
Effective assessment combines at least two of the above methods to reduce false negatives. Regular monitoring after treatment, typically every 7–10 days for three successive checks, ensures eradication and prevents re‑infestation.