A total of 548 food handlers from 14 catering establishments
located throughout Hong Kong were nasally swabbed by a trained
researcher using a moistened transport swab on 2 occasions, 3-6
months apart, to define nasal carriage status. Swabs were transferred
to the laboratory for culture within 2 hours of collection.
Persistent carriers were defined as individuals with both specimens
positive with the same spa type, whereas those positive on 1
occasion were classified as transient carriers. On the second visit,
direct fingertip imprint specimens were collected. For any establishment
where hand contamination rates exceeded the average by
10%, sampling was repeated 1 month after reinforcement of
handwashing training.
Ethical approval was obtained from the University Ethics Committee.
Each subject was provided with an information sheet and
gave written consent.
Nasal swabs were incubated overnight in 5% salt-supplemented
brain-heart infusion broth (Oxoid, Basingstoke, UK) at 37
C before
subculture onto SA Select agar (Bio-Rad UK Ltd, Hemel, Hempstead,
UK). Imprints of fingerprints of the dominant hand were obtained
on mannitol salt agar (Oxoid). Isolates were confirmed as S aureus
by latex agglutination (Remel, Lennexa, Kan) and characterized by
spa typing and comparison with the Ridom database.
5
To determine
the degree of similarity of strains, Simpson’s diversity index (D)was
calculated using standard formulae.