R. J. Fletcher quotes selectively (South China Morning Post, February 26) from an editorial in the British Medical Journal (February 12) on air quality in passenger aircraft. I would like to make a few observations on his claims that the editorial supports the cause of the tobacco industry, that its author is better qualified than either he or I to make judgments on the issue and his castigation of me for not consulting the editorial before I wrote. Wing Commander Harding's BMJ editorial, published after I penned my letter, is a useful summary of some problems in the assessment of the cabin environment. However, I and many others in public health and aviation medicine would not agree with the wording of his final statement that ''it is reasonable to conclude that environmental tobacco smoke (ETS) . . . does not represent a great threat to health''. I believe that he was trying to reflect the fact that we do not have data on chronic health effects specifically from long-term prospective studies of air crew and passengers. Such studies might be attempted but would be difficult for a number of reasons and in terms of measuring the cumulative effects of repeated exposures to ETS they would be ethically undesirable and analogous to re-inventing the wheel. There is ample evidence now that the safest decision is to protect crew and passengers from any additional risk. In Hong Kong we certainly do not need any more data to establish the risk of ETS exposure in infants and young children who, as your correspondent C. S. Barron (Post, March 4) points out, are a particularly vulnerable group. I spoke to Wing Commander Harding about these issues and told him that the tobacco industry had hijacked his piece and used it to support its arguments against smoke-free flights. He was disappointed to hear that and pointed to another statement he made in the article, that ''of course, a total ban on smoking on all aircraft would instantly improve matters subjectively, and such measures are being considered''. He also authorised me to state on his behalf that, ''smoking on aircraft is highly undesirable and the best solution would be to ban it''. One of the key references in the BMJ editorial was unfortunately a biased rehash of previous reviews and studies, authored by two private environmental consultants who are well-known supporters of tobacco industry activities. One of them in particular has appeared for the industry in the US and other places for many years. In 1989 he was quoted by the industry in Finland and Denmark in a campaign against airline smoking restrictions. In May 1992, the same consultant appeared in Hong Kong at a tobacco seminar on ETS, for the media, from which medical personnel were excluded. He later went on a radio phone-in programme and attempted to refute the evidence on ETS effects in children. I have pointed out to the British Medical Journal editorial office that this is not the stuff from which independent scientific evidence can usually be derived. They agreed and said that they had already questioned the provenance of the article. The continuing attempts of the tobacco industry to sponsor ''studies'' and have them published in quotable sources threatens to corrupt the scientific literature on smoking-related diseases. Without vigilance they could feed through to policy making in the public and private sectors; precisely what is intended. In the meantime I believe Cathay's customers continue to vote with their bookings. A. J. HEDLEY Professor of Community Medicine University of Hong Kong
