Dick Reaction

DICK REACTION (Dick), named after the Dicks, who proposed it for determining susceptibility to scarlet fever. These American researchers consider the causative agent of scarlet fever to be a special type of hemolytic streptococcus, which, primarily localizing in the pharyngeal mucosa, secretes a toxin that poisons the infected organism. To obtain the toxin, the scarlatinal streptococcus is grown on meat-peptone broth. The Dick reaction is based on the same principle as the Schick reaction in diphtheria, namely, that a positive reaction, i.e., characteristic redness at the site of injection, occurs only in people susceptible to scarlet fever (see); a negative reaction, however, indicates the presence of antitoxin in the blood and therefore indicates insusceptibility to the infection. For the Dick reaction, one skin dose of toxin is strictly injected intradermally, i.e., that minimal amount which still gives a clear reaction in susceptible subjects (technique—see Intradermal reaction). In January 1928, Glennie, Waddington, and Pope proposed a buffer mixture consisting of 57.0 Borax cryst., 84.0 Ac. boric, and 99.0 Natr. chlorat. A 1.5% solution of this mixture in distilled water is used to dilute the toxin. This solution has a pH of 8.0-8.4 and does not decompose during autoclave sterilization. According to observations by these authors, the toxin diluted with buffer solution retains its potency for 6 months. Control experiments by Krestovnikov completely confirmed this. In positive cases, the reaction appears 4-6 hours after injection and reaches its maximum after 18-24 hours, after which the redness gradually fades and disappears by the end of 3-4 days. The reaction has a vascular nature and, according to some authors, is caused by paralysis of the skin's vasomotor nerves (Jungeblut). It is never accompanied by tissue necrosis and rarely leaves pigmentation after it. Adding adrenaline to the toxin weakens the reaction until it completely disappears, while caffeine enhances it. By these properties, the Dick reaction differs from the toxic Schick reaction and approaches allergic reactions (tuberculin, etc.) and the false Schick reaction (Groer). For control, scarlatinal toxin heated for one hour in a water bath at 100° is used. If purified toxin according to Hunt is used, control injection is unnecessary, as a false reaction occurs in no more than 2% of cases (Korshun and Spirina). The reaction is read 18-24 hours after the injection in diffuse daylight. Unclear weak redness with a diameter of less than 1 cm is recorded as a doubtful reaction and is considered equivalent to negative in significance. The degree of positive reaction is denoted by crosses—one, if the diameter of the redness is not more than 2 cm, two, if it reaches 2-3 cm, and three, if it exceeds 3 cm and is accompanied by significant infiltration. There is no rise in temperature or any general symptoms. Additionally, the following are distinguished: false reaction, when redness of the same degree is obtained from both active and boiled toxin; combined, when redness from active toxin is stronger than from boiled toxin; and finally, perverted, when redness from boiled toxin is stronger than from active. The frequency of positive reaction depends on age. Thus, according to data by Zingher, it occurs in children under 6 months of age in 44.8%, 6 months-3 years in 64-71%, 3-5 years in 46-56%, 5-20 years in 24-37%, and in adults in 18% (Keg, McCartney, McGarrity). These data are generally confirmed by research in other countries. In the study of 42,284 preschool and school-age children in 1926-1927 (during epidemic time), 45.9% positive Dick reactions were obtained in Moscow (Korshun and Spirina). In the first 3 days of illness, the Dick reaction is positive in the vast majority of scarlet fever patients, but as recovery progresses, the percentage decreases. According to Schottmüller (1928), from 91.0 in the first days of illness, the percentage of positive reactions decreases to 2.3 at discharge from the hospital, and according to older data (1925—Keg, McCartney and McGarrity)—from 73.9% to 10.6%, while in those who have had scarlet fever, it is 20%. From this it follows that almost exclusively persons with a positive Dick reaction contract scarlet fever, which in most recovering patients, i.e., with the development of immunity, becomes negative. The influence of the social factor on the frequency of positive Dick reaction is noted, quite similar to that established for the Schick reaction. Namely, children from less affluent strata of the population, living more crowded and in worse sanitary conditions, give a significantly lower percentage of positive Dick reactions than children from more prosperous parents. The former, coming into contact with infection more often, have more chances to acquire immunity due to the 'unnoticed' immunization that occurs. Most authors recognize that a positive Dick reaction indicates susceptibility to scarlet fever, but the reaction can change its character upon retesting in the same subject without any apparent reason; cases of scarlet fever disease have even been noted with a negative Dick reaction. Therefore, some authors consider a positive Dick reaction only as an expression of increased sensitivity of the organism to streptococcal products due to prior sensitization. According to this view, a negative Dick reaction does not prove the presence of antitoxin in the blood and therefore does not indicate insusceptibility to scarlet fever. The assertion of some authors that non-specific materials (e.g., typhoid vaccine, Miner-vin) can, upon immunization with them, turn a positive Dick reaction into negative, is considered controversial and requires further verification. As new research by Rubasheva, Yakobi, and others shows, the Dick reaction can apparently be used for prognostic purposes. It has been established that children belonging to the same blood group as the parent who has a positive Dick reaction necessarily also have a positive reaction and retain it despite vaccination and even after having scarlet fever. Such children have a more severe course of the disease. These observations coincide with observations on the Schick reaction.