The caduceus as lifeguard

Between 1991 and 1994, the University Teaching Hospital in Lusaka reduced the proportion of collected blood units testing HIV positive from 20-3% to 7-0% (Watts C, Goodman H, unpublished). This reduction was achieved by a change in blood-collection policy-reorientation of blood collection away from replacement donors (usually relatives of the patient requiring transfusion) in whom HIV prevalence proved high, and towards collection from voluntary donors at schools and colleges, in whom HIV prevalence is low. Care is needed when estimating this impact on HIV infections averted. For example, if transfusions were made to 500 susceptible people, one could estimate that HIV screening of blood potentially averted at most 35 HIV infections in 1994 and 102 infections in 1991 (assuming HIV prevalence figures 7-0% and 20-3%, respectively). Consequently, one could reach the perverse conclusion that the hospital was averting almost three times as many HIV infections through testing its donated blood in 1991 than it did in 1994, even though substantial reforms in blood-collection procedures had been implemented in the interim; this is because estimates of the prevalence of HIV in the donor population alone have been used to estimate HIV infections averted, rather than taking account of the combined impact of the many aspects of the delivery of safe blood. In this case, the smaller figure would represent the number of HIV infections averted solely through screening blood for HIV. The larger figure would more closely represent the number of HIV infections averted by both selectively recruiting low risk donors and screening blood. Similarly, the impact of reducing the number of unnecessary blood transfusions could be inadvertently underestimated. A 10% reduction in transfusions could lead to the conclusion that up to 10% fewer HIV infections had been averted, when in fact the reverse would be true. This argument illustrates that care should be taken in calculation of the impact of blood safety measures on averting HIV infections. We are working with the WHO/Global Programme on AIDS to develop standardised methods to estimate the combined impact of the selective recruitment of low-risk donors, as well as the reduction of unnecessary transfusions and screening of blood for HIV. We hope that these techniques will enable the impact of strengthening blood transfusion services as a strategy for HIV prevention to be fully appreciated. Charlotte Watts,

*Hilary Goodman, Gabriel Muyinda

*Health Policy Unit, London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK; and Zambia National Blood Transfusion Service, Lusaka, Zambia

1

Beal RW, Bontinck M, Fransen L, eds. Safe blood in countries. Brussels: EEC AIDS Task Force, 1992.

Figure: Snakes

Kitapçi, Ayca Ciftci, I Safa Kaya,

Departments of *Anaesthetics and Paediatrics, Turkish Health and Therapy Foundation Medical Centre Hospital, Emek 06510, Ankara, Turkey

developing 1

Bunn JT. Origin of the caduceus motif. JAMA 1967; 202: 615-19. Daves ML. Snake wars. Radiology 1994; 192: 140. Köker AH, ed. Gevher Nesibe Sultan Medical School (Erciyes Univ Med Hist Inst Publ no 10). Kayseri, Turkey: Erciyes University Medical History Institute, 1991.

lifeguard

SiR-The origin of the caduceus, the symbol of medicine, has intrigued physicians for centuries. Ignoring the healing snakes of the ancient Egyptian, Minoan, and Chinese cultures, the consensus is that the origin lies with Aesculapius, one of the original 12 Olympians and the demigod of medicine, healing, and physicians. He carried a sceptre with a snake wound on it. The caduceus of Apollo, god of healing, light, and beauty, to whom the ancient Greek physicians swore when they took the Hippocratic oath, had two snakes.2 Apart from the rumour that its poison has healing properties why has the snake become the symbol of medicine? The explanation may in part lie in the beliefs of pre-Islamic (Shaman) and Islamic cultures. The ancient 784

tree of life

of

*Mete F Toppare, Füsun D Ali Senses

3

as

guards of the

Middle Asia-the so-called celestial Turks and their predecessors of the Seljuk Empire in (Gokturk) Asia Minor (Anatolia)-had a folkloric appreciation of snakes. Only an animal as dreadful as the snake could adequately protect the tree of life. An illustration on a Seljuk drum (figure) shows two snakes as guards of the life tree. This motif is in the Gevher Nesibe Sultan Museum and School of Medicine (named after the sister of the Seljuk emperor Giyaseddin Keyhusrev) in Kayseri, mid-Anatolia. The medical school was founded in 1206 AD, when medieval Eastern medicine dominated medical education and famous physicians like Razeh and Ibn Sina (Avicenna) had great influence on treatment. The Gevher Nesibe school, still in good condition and open as a museum, used to have many similarities in teaching style to medical schools today. It had preclinical and clinical branches in separate buildings,3 and the entrance to the clinical section also bears a large snake motif. Perhaps we should think of snakes as signs of protection of life not just as mythological symbols of the medicine of Ancient Greece.

Turks

2

The caduceus

as

DEPARTMENT OF ERROR New WHO family planning guidelines-In this news item (May 27, 1358), the consensus of the expert group was that, except in rare circumstances, combined oral contraceptives should contain "less than 50 flg oestrogen" (not "no more than 50 ).tg").

p

Hypoglycaemia m spinal muscular atrophy-In this short report by Anne K Bruce and colleagues (Sept 2, p 609), the penultimate sentence of the first paragraph on page 610 should have read "lactate dehydrogenase"and not "luteinismg hormone". Clindamycln and pseudomembranous colitis-In this letter by Riley and Golledge (Sept 2, p 639) the word "not" was left out from the second sentence of the last paragraph, which should have read "The other is exposure to the

develop".

organism,

and if this does

not occur

then CDAD will

not