The significance of the pseudoreaction in the Dick test and methods used for its identification.

Pseudoreactions due to the autolyzed streptococcus protein and other protein constituents of the toxin broth test fluid have an important bearing in the interpretation of the Dick reaction. Of 589 children tested in one of the public schools 459 were found to be immune. Of these, 190 or 41.4 per cent gave a pseudoreaction. Of the 130 susceptible children, 45 or 34.6 per cent gave a combined positive and pseudo reaction. Of another group of 950 children, who received the Dick test in two institutions, 686 were found to be immune. Of these, 232 or 33.8 per cent gave a pseudoreaction. Of the 264 non-immunes, 90 or 34.0 per cent gave a combined reaction. In children under 5 years the percentage of negative pseudo and positive combined reactions is much less and is closely analogous to the similar small percentages of pseudo reactions found with the Schick test in this age group.

To make the readings of the Dick reactions more accurate and avoid the confusion that is very likely to arise between positive and negative pseudoreactions it is important to use a control test, which will show with a great deal of accuracy the difference between the four different reactions described before this society at its March meeting in connection with the Dick test: the positive, negative, negative pseudo and positive combined. The control test is thus closely analogous to the one used with the Schick test and serves the same purpose. It is even more important, however, to use a control with the Dick test than it is with the Schick test where it is strongly indicated in older children and adults. As the positive reactions appear within 24 hours the time element used by some to separate the positive and negative pseudoreactions in the Schick test is practically of little or no value in differentiating the reactions noted with the Dick test.