999LEADING ARTICLES

Salmonellas in Meat

THE LANCETLONDON 7 NOVEMBER 1964

THAT meat and meat products are every year thecommonest single source of salmonella infections hasbeen clear since the first annual report on food-poison-ing from the Public Health Laboratory Service. Largelocalised outbreaks have been easily recognised sinceGAERTNER’S day, but from time to time careful investi-gations have .shown that meat from a single source hascaused sporadic infection over a wide area. Evidencefrom two large cities demonstrated some connectionbetween the salmonellas isolated in the abattoir andthose found in the population. Two purely bacteriolo-gical factors have helped these studies. Nowadays thevariety of salmonella serotypes in circulation in this

country is far greater than formerly and, thoughSalmonella typhimurium still outnumbers all the others,typing by bacteriophage allows the investigator to

identify a strain with some certainty. Tracing a chainof infection is easier than it was.

It was against this background that a committee ofthe Public Health Laboratory Service investigated the

. bacteriology of abattoirs and butchers’ shops; andtheir report 1 makes disturbing reading. Both kindsof premises were sampled for salmonellas by culturingMoore swabs which had been left in the effluent drains.This may seem a rough-and-ready method, but it

probably gives a reasonably comparable estimate of thenumber of infected animals which have been slaughtered.Over two successive years 930 (20%) out of 4496 Mooreswabs from 32 abattoirs in England and Wales yieldedsalmonellas. Neither the site of the abattoir nor its sizeseemed to bear any relation to the percentage of isola-tions, but in general those which gave a low yield in thefirst year did the same in the second. Slaughterhouseshandling large numbers of cattle gave more salmonellasthan those in which sheep preponderated. Baconfactories (killing only pigs) gave high figures, even

though the typical parasite of pigs, S. choleraesuis, wasnever found (probably for technical reasons). Theexamination of specimens of mesenteric glands, spleen,and liver from the abattoirs yielded, as might beexpected, a lower proportion of positives, but 218isolations from 11,347 specimens cannot be disregarded.By these standards drain swabs and tissue specimensfrom butchers’ shops were relatively unproductive, butthey gave unequivocal evidence that every day manyhousewives are meeting salmonellas face to face. It isfortunate that raw meat is not to our national taste.These figures are hard to assess quantitatively. The

1. J. Hyg., Camb. 1964, 62, 283.

proportion of individual animals found to be infectedis so much greater than any estimate of the incidenceof salmonellosis in living animals that some explanationis desirable. Every veterinary surgeon (and everyfamily doctor) will admit that some salmonella infectionsnever come to their notice. It has been shown that

feeding pigs with foodstuffs naturally contaminatedwith salmonellas is not necessarily followed by disease.2The organisms were recovered from the faeces for ashort time and small numbers were found in the mesen-teric glands, but none at any time in the muscles.Nevertheless we must accept that the figures given inthe P.H.L.S. report show that the consumer runs risksof which he never dreams, and this is confirmed by themany examples given of the spread of infection fromthe butcher’s shop to the public at large. Defective

hygiene can spread infection from a single source farand wide within the shop.3Ways of protecting our fellow citizens from this

danger might be easier to suggest if people were moreinterested. It seems to us that protection must start atthe abattoir. Every cow and pig carcass should beexamined bacteriologically and held in cold store untilshown to be free of salmonellas. Today this is obviouslyimpossible.

" Abattoir " may mean a modern buildingwith large cold stores handling several hundred animalseach week or a shed in the corner of a field used oncea fortnight. (It was misguided political enthusiasm andnot regard for the public health which led to theabandonment of a rational plan to provide centralisedmodern abattoirs for the whole country.) The meattrade is uncommonly individualistic and does not takekindly to suggestions from outsiders. Our system ofmeat inspection is not as good as it should be. We lackas yet the bacteriological knowledge needed for a reallyworkable system of examination. Is it possible to devisea single (or perhaps double) culture method which willshow to the limit of legal proof that a carcass is free ofsalmonellas ? Is it certain that the presence of salmonellasin the abdominal viscera shows that they are also in themuscles, which are, after all, what most of us eat ? If

not, it might be possible to separate and sterilise theoffal before it leaves the abattoir. One argument againstbacteriological tests of safety is that they take time; andit has been suggested that immunofluorescence mightgive quicker answers than the present culture methods.4 4As they stand at present, these methods could be nomore than a screening test (and not an entirely reliableone at that), but there is every likelihood that they willbe improved.

Before anyone can envisage practical measures to

remove this risk to health, there is a lot of work to bedone. There are now almost certainly more deaths fromsalmonella infections (excluding enteric fever) than frombovine tuberculosis: there are many hundred times asmany infections. Some of the money and time whichare now spent on the examination of milk from tuber-culin-tested herds for tubercle bacilli might be more

2. Smith, H. W. ibid. 1960, 58, 381.3. Camps, F. E. Mon. Bull. Minist. Hlth Lab. Serv. 1947, 6, 89.4. Georgala, D. L., Boothroyd, M. J. Hyg., Camb. 1964, 62, 319.

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usefully employed in detailed quantitative studies ofthe postmortem survival of salmonellas in cows and

pigs and in practical trials of routine bacteriologicalexaminations in the abattoir.

Cardiac PunctureTWENTY years ago the suggestion that the heart should

be deliberately punctured by a needle for diagnosticpurposes would have been judged exceedingly rash.Accidental puncture during pericardiocentesis was

accepted as a necessary risk, certainly to be avoided ifpossible; and intracardiac injection by direct puncturewas occasionally part of the desperate resuscitation of adying patient. The development of cardiac surgery hasnow brought a better understanding of what may reason-ably be undertaken in this direction; and it has at thesame time created a need for more precise knowledge ofthe function of the heart in many conditions. Catheter-isation of the right side of the heart by the venous routehad already been introduced and was developed furtherin response to this need, but it generally provided littleinformation about the left side of the heart. Investigationof the left ventricle by retrograde catheterisation throughthe aorta was shown to be feasible 2 but it has itslimitations in risk and technical difficulties, and theinformation it yields is often inadequate.Many techniques involving needle puncture of the

heart have since been developed. PONSDOMENECH andNUNEZ 3 were early pioneers when they performed directventricular puncture for angiocardiography; but theywere perhaps ahead of the times, for their report appar-ently aroused little enthusiasm for cardiac puncture.The close anatomical relation between the beginning ofthe left bronchus and the left atrium led to the successfultrial of direct puncture of this chamber by a long needleintroduced along a bronchoscope.4 5 This techniquewas established as feasible and safe, but it was later

superseded, chiefly because it depended upon initial

bronchoscopy. Using the right paravertebral approach,percutaneous puncture of the left atrium, and explorationof the left ventricle by a fine catheter passed through theneedle, has proved satisfactory; but it has been criticisedbecause of the hazards and because the patient has to beplaced in the lateral or prone position. Percutaneous

puncture by the suprasternal approach 8 was an alterna-tive, and often permitted puncture of the aorta andpulmonary artery en route 9; to puncture these vessels,however, a fine needle had to be used to reduce bleed-ing and this precluded catheterisation of the left ventricle.One attempt to overcome these difficulties was the

ingenious device of puncturing the left atrium transsept-ally from the right by a needle introduced through acatheter already inserted from the saphenous vein into1. Zimmerman, H. A., Scott, R. W., Becker, O. N. Circulation, 1950, 1,

357.2. Limon Lason, R., Rubio Alvarez, V., Bouchard, F. Arch. Inst. Cardiol.

Mexico, 1950, 20, 271.3. Ponsdomonech, E. R., Nunez, V. B. Amer. Heart J. 1951, 41, 643.4. Facquet, J., Lemoine, J. M., Alhomme, P., Lefebvre, J. Arch. mal. cœur,

1952, 45, 741.5. Allison, P. R., Linden, R. J. Circulation, 1953, 7, 669.6. Bjork, V. O., Malmström, G., Uggla, L. G. Ann. Surg. 1954, 138, 718.7. Bjork, V. O., Blakemore, W. S., Malmstrom, G. Amer. Heart J. 1954,

48, 197.8. Radner, S. Acta med. scand. 1954, 148, 57.9. Radner, S. ibid. 1955, 151, 223.

the right heart 10-12; the patient lies supine and nopuncture of the external wall of the heart is involved.This technique has been modified to allow a catheter tobe guided over the needle and advanced to the leftventricle.13 Experience has shown the versatility of thismethod, and it is particularly suitable for left heart

angiocardiography; but the needle or catheter may passoutwards through the wall of the heart, and it is doubtfulwhether this procedure is significantly safer than some ofthe others.

Direct percutaneous puncture of the left ventricle

through the apex of the heart for the assessment of aorticstenosis was reintroduced by Sir RussELL BROCK and hiscolleagues.14 A fine catheter can be passed through theneedle into the aorta in nearly all patients, even thosewith severe stenosis. The technique’s chief limitation isthat the needle can be kept in place for only a short time,in order to avoid undue risk.15 But the method is

simple, the success-rate is high, and the risk is acceptablein competent hands.

LEVY and LILLEHEI 16 now report a modification of theventricular puncture which promises to retain the meritsof the original while enlarging its scope. Using a stylet,they introduce a fine metal cannula by direct anteriorpuncture of the left ventricle. A closely fitting tefloncatheter, which has been previously slid over the

cannula, is then pushed forwards into the ventricularcavity. A flexible stylet can then be passed through thecatheter, allowing it to be passed backwards into theatrium or advanced to the aorta. After studying thepossibilities in animals, they used the technique in 122patients with various forms of congenital and acquiredheart-disease; in 5 cases the right ventricle was also

explored by this method. Angiocardiography can beperformed through the catheter, but that means fixingthe catheter to the skin to prevent it recoiling during therapid injection of contrast medium; this happened in onepatient and led to the only death in the series. Tam-ponade was precipitated in another patient, but peri-cardial aspiration relieved it. In two cases the flexible

stylet broke, and operation was necessary to remove theretained fragment: this misfortune was attributed to afault in the design of the stylet, which has now beencorrected. This technique offers the prospect of leftventricular angiocardiography in conjunction with directventricular puncture; and if this can be done safely, itwill be a valuable addition to methods of cardiac

puncture.While new methods of puncture are often advocated

as improvements that should replace older techniques, itis probably better to assess each in terms of the clinical

‘ problem it can best answer. All have risks, but these can

’ be small when the puncture is performed by a skilled’

operator, and their application to seriously ill patients10. Ross, J., Jr. Ann. Surg. 1959, 149, 395.11. Cope, C. J. thorac. Surg. 1959, 37, 482.12. Ross, J., Jr., Braunwald, E., Morrow, A. G. Amer. J. Cardiol. 1959, 3,

653.13. Brockenborough, E. C., Braunwald, E., Ross, J., Jr. Circulation, 1962,

25, 15.14. Brock, R., Milstein, B. B., Ross, D. N. Thorax, 1956, 11, 163.15. Bjork, V. O., Cullhed, I., Hallén, A., Lodin, H., Malers, E. Circulation,

1961, 24, 204.16. Levy, M. J., Lillehei, C. W. New Engl. J. Med. 1964, 277, 273.