Some problems connected with the Dick test / by R,A, O'Brien and C.C. Okell.

  • O'Brien, Richard Alfred, 1878-1970.
Date:
1925.]
Catalogue details

Licence: In copyright

Credit: Some problems connected with the Dick test / by R,A, O'Brien and C.C. Okell. Source: Wellcome Collection.

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    4 while a 1/1000 dilution gave 00 per cent, of positive reactions ; for the second week the figures were 6 per cent, and 12 per cent. It is therefore evident that 1/1000 is the better strength to use when testing patients considered to be suffering from scarlet fever. It may, of course, not be the optimum. Percentage of Positive Reactions. Different observers, when testing patients admitted in the first two days of the disease, have obtained different percentages of positive reactions. Most workers give a percentage of from 66 to 100, while two clinicians, working with small groups of patients, obtained percentages as low as 22 and 42. Probably a close study of these differences would give informa¬ tion of value. The change from a positive to a negative response to a 1/1000 dilution of the toxin during the disease appears to occur in the average case about the fifth to the eighth day. One point of some interest is that amongst 673 reactions there were but 10 (1-5 per cent.) “ pseudo and positive,” and 25 (3-7 per cent.)“ pseudo and negative.” This low percentage we probably owe to the fact that Okell and Watson chose for the growth of the streptococcus ordinary digest medium containing no blood, and, from a study of the growth and metabolism curves, harvested the toxin at 18 hours. With a 1/1000 dilution of toxin the percentage of positive reactors in different ward staffs varied from 7-5 in a large hospital (106 nurses) to 10 amongst 31 nurses and probationers. Evidently the great majority of nurses of long experience in scarlet fever wards are negative to the Dick test and non- susceptible to the disease. We do not know accurately what percentage of nurses in such wards would give a history of having contracted scarlet fever during their hospital life. It is probably fairly large, but many have no such history. Evidently, as in diphtheria, nurses (and others) may become immune through minute unrecognised infections with the scarlet fever organism. Nurses with positive reactions are generally newcomers. Two nurses in fever hospitals who gave a positive response to the test developed scarlet fever later. We would not be surprised to find that practically every nurse who has been several years in scarlet fever wards has either suffered from an attack of the disease during her hospital career or has already become immune from unrecognised infections either during or prior to life in the wards. Significance of a Negative Response. We know broadly that a negative response to the Dick test indicates a high degree of non-susceptibility,