Your data briefing on hospital infections (page 37, 2 November) is a serious cause for concern.

In the early 1980s, following a review of some 8,000 operations, Lidwell et al published reports about sepsis following total hip and knee-joint replacements.

They found that the typical post-operative wound infection rate in conventionally ventilated operating rooms was 3 per cent.

The use of ultra-clean ventilation systems halved this.

Special clothing systems and antibiotics were found to reduce this infection rate further.

Since then, conventional operating room ventilation has improved significantly, and many more ultra-clean ventilation systems have been installed.

The reported figures of infection in England in 1999 for hip prosthesis (3 per cent) and knee prosthesis (about 2.5 per cent) would seem to indicate, given better ventilation systems - and indeed more specialised antibiotics - that either Lidwell and his colleagues could not do their sums, which I doubt, or that the situation is worse than the statistics suggest.

LWM Arrowsmith Arrowsmith and Associates Bromley Kent