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VOL 341: APRIL 17, 1993 TIHE LANCET 993 / Do epidemiologists cause epidemics? Two young epidemiologists confidently announced over the radio that an epidemic of influenza would soon reach their country. Deaths attributed to influenza immediately rose, as doctors started to diagnose influenza as the terminal illness in their elderly and infirm patients. Some time later people realised that the epidemic had in fact never reached the country and that the rise in influenza death rates was matched by a deficit in deaths ascribed to pneumonia. This tale, popular among teachers of epidemioiogy, is difficult to verify, and may well have been embellished in the tradition of story telling. However, occasionally stories come true. A provincial cancer registry issued a warning that cancer rates were increased in an area that had been under environmental suspicion for some years.' The popular press responded with dramatic headlines. Real estate (property) prices fell; the inhabitants reported health problems among friends and neighbours and contemplated moving, even though individual respondents showed more resilience in their health beliefs. On review, it was found that a wrong denominator had been used a mistake that • , could easily happen because the reporting of population figures did not follow the same administrative boundaries as the cancer registry. In retrospect, the episode can even be turned to our advantage, because it pro-vides an opportunity to learn about the "placebo" part of a community's response to a perceived cancer risk. Even in the absence of panic about industrial waste, epidemics may become partly self-fulfilling. In all probability, physicians started to designate an ever- increasing proportion of unexplained sudden deaths in elderly persons as "coronaries" when awareness of the "epidanics of affluence" grew.2-1 After all, one diagnoses what one believes is common. Elementary mistakes do occur. Thus, another publicity disaster was narrowly averted when a neighbourhood said to have very high cancer rates- again in relation to to~dc waste--was found to contain mostly elderly inhabitants. Simple age standardisation dispelled the worries. To confound matters further, the public's reaction is unpredictable. In the Netherlands, the well-meaning advice of health authorities to remove the upper layers of cadmium- contaminated garden soil (a legacy of the industrial revolution of bygone times in an area in the south of the country) met with stiff popular resistance. An action committee was formed to dispute the epidemiological findings. As the inhabitants pointed out, their fathers had already lived from the fruits of these gardens, so why should the gardens be destroyed in this way}`s The arguments of the action committee did not prevail, however, and finally almost everyone complied. One difficulty with epidemiology is its popularity with editors, both medical and in the tabloid press. Epidemiological data make such easy headlines, which everyone can understand and is entitled to have an opinion about "coffee causes cancer"; "breast cancer on the rise"; and so on. The reaction of the professionals is often one of annoyance-why don't all these people see that mere commonsense is not enough? People seldom think they are entitled to opinions about the results of the latest DNA- gimmick, so why do they think they can meddle with epidemiology? Still, quick and easy fame is attractive to epidemiologists. This is not merely to do with personal ambition or desire for more fiuiding; often there is a genuine wish to improve the public's health. More than a decade ago, leaders of the profession ideatified a potential credibility problem with publishing "week after week of cause after cause", and counselled restraint 6 As part of the remedy, others propose that epidemiological science should be kept scrupulously apart from policy-making.' Scientists and policy-makers have different agendas and responsibilities. Health policy might move ahead, even in the face of scientific uncertainty. Conversely, scientific criticism should never be thwarted berause a policy decision seems necessary. An example of responsible reporting is to be found in a paper by Thorogood et al° that highlighted an increase in fatal myocardial infarcrion among young women who used psychotropic drugs. These

TlE LANCET VOL 341: aPRIL 17, 1993 researchers pointed out that the finding was unexpected, that it was the result of a secondary analysis in a study done for other reasons, and that there might be a host of alternative explanations. Such findings should be published, and not suppressed, however unlikely, since unexpected results can contain grains of future truth. However, neither editors nor authors should fall into the easy-headline trap. Similarly, the finding of an astonishingly high adverse reaction rate with a new drug or procedure is more likely than not the joint effect of a real underlying problem and some bad luck-a "random high"-in a series of patients. Yet it is this "random high" that brings the problem to attention, even if the exact incidence in the first report is probably an overestimate.9 As everywhere in medical science, the urge to rush into print and announce epidemics should be tempered by critical realism and self-criticism, which is often helped by discussions with sympathetic but dispassionate outsiders; one is always inclined to • overlook one's own elementary mistakes and biases. Even with these precautions, disease trends that might be influenced by diagtostic fashion will always be difficult to evaluate. Their interpretation demands a healthy degree of scepticism and more than a passing acquaintance with the history and development of medical knowledge. The Lancet • 1. Guidom TL. Jacobs PH. The uaplianons ofan epidertuolo®al nusnice: a maunutury's response to a pesenaed eccess ancu nsk. Am J Pr+ol Hralrh 1993; 83: 233-39. 2. Scehbeu WE. Anapprasaloftheepideavcrtseofcvevoar}•heottdisose and its decline. l.auir 1987; i: 60G-11. 3. T'homas e1C, Knapman PA, Krikkr D.M. Davxs N J. Commuwty study of the auses of "nanus!" sudden deuh. B.1fJ 1988; 297: 1453-55. 4. Kress I. CAdtruum mntaminaaoe of the caanayside: a ose study on health effects. Toam! rnd Hcafrh 1990; 6: 181-88. s. Gooding K. "I7ure'a something nssry at the bottom of the Qatden. FSimaal Tiine 1992; June 6.7: VII. 6. Keisey J. Cited in: -Outgomg SER president :lddtases Cuusnnae -Meeang". Epide,ad Slaora 1982; 3: 2. 7. Rothmsn KJ, Poole Qi. Sdmce and po4cY making. Av J P::bi Hrak6 1985; 75. 344-f 1. 8.'IZw:ogood tit, Cowers PH, Jtaan J, Murphy M, Ve:sev >.L Fatal myonrdial infarcoan and use of psydioaoptc drugs in young Komen. lancet 1992; 381k 1067-,8. 9. Editorul. Disesu dute:ing: hide or seek.l, 1~:++cu 1990; 336: 717-18. INFECTIOUS DISEASES Mumps vaccination and meningitis Mumps infection is not merely a nuisance; it can be fatal. 'rhere are epidemics every 2-3 years and the virus spreads so readily by droplet infection, direct contaa, or fornites that 80-W% of adults have viral antibodies unless they live in isolated communities. Mean incubation period is 16-18 days, and symptoms and signs develop in 60=~ 0% of those infected 'Ihe initial febrile illness with parotitis is uncomfortable but the most serious aspect of mumps is the cotnplicstions. Mumps used to be the commonest cause of viral meningitis and encephalitis in many countries, being responsible for 36% ofall infectious encephalitides reported in the L: Sr1, for exatnple.j T'hus, the frequencyofineningiris is oftes; said to be I per 1000 cases of clinical mumps, but much higher figures have been observed during epidemics. In 1971-81 in England and Wales, at leasj,16 individuals died fimm mumps, 13 of them as a result of encephalitis? Military reauits are at special risk of epididymo-orchitis, and tlus complication affects as many as 38% of postpuberral boys and men with clinical illness.' :biumps is an important muse of male infertility and used to be the commonest tzuse of acquired deafizess in c~tildhood.' Conditions such as pancreatitis, diabetes, fatal myorarditis, and abortions have also been attributed to this paramyxovirus infection. For all these reasons, researchers turned their attention to immunisacion. The first attempt at mumps immunisation was probably that of Barla-Szsbo and Krarnir in the late 1920s. These Hungatian workers gave young mm defibtinated blood 5rom patients with mumps by intracutaneous injection, or convalescent serum intramuscularly. Some protection was achiered in both instances, as also was the case among Finnish recruits during the 1939-45 war. The first, fotmalin-inacdvated, vaccine was developed in the 1950s, and proved so succ~ssful (94% reduction in incidence) that it wzc adopted for routine use by the Finnish defence forces in 1960. A killed vaccine was also used in the USA during 1950-78. Meanwhile, live virus vaccines were developed in the L: SA and the Soviet Union. Since the emphasis in public health circles was on combating measles and rubella, mumps vac.-ine was adopted in the USA from 1967 oonwards very gradually (as monovalent or bivalent vaccznes) until the nzcaknt measles-mumps-rubella vaccine was rt:romrnended as the preparation of choice in 1980. The justification for incorporating mumps with two other components was that, should vaccine uptake remain low (<70°;i, the incidence of orchitis would eventually incaeise, not deaea.se.' Several European countries likewise launched mumps- measles-rubella vaccinations, with considerable impact. The incidence of mumps is now a fraction of its former seif,' and meningitis and encephalitis have been virtually eliminated.° Motmver, there are few adverse reactions to the vaccine. Hou•erer, there are now a few clouds on this otherwise bright horizon. In the vaccine adopted by the USA, Scandinavia, and some other areas the Jeryl Ldnn B strain is used as the mumps antigen, whereas in other countries, including the UK, vaccines with the Japanese Urabe AM 9 strain are or were marketed. Since both strains are neurotrapic, albeit to a mudi lesser mctent than natural virus, some omtral nervous systetn manifestations would not be unecpeszed. In 1989 the Immunization Practices Advisory Committee in the USA estimated that the incidence of postvaccnation encephalitis within 30 days was 0•4cases per 1 million doses administered.''Me figure was subsequently challenged by reports of meningitis for which there was no possibilitt of natural infection as the underlying causc--ie, the virus isoiated from cerebtospinai fluid %%as identified by nudeotide sequences as the same as in the vaccine. A common feature was that the strain was repeatedly Urabe. Although one cannot conclude from this that Jeryl Lynn would be free of such side-effects,'ao all the evidence points towards a considerable difference between