Previous to the present time the author has been unable to find records of investigators having used this method of studying influenza to any appreciable extent. Certainly there has been nothing done on the subject previous to the last pandemic. Since then Frost has studied, as indicated in his report, family incidence to the extent of determining the relationship to overcrowding and to economic status, and Niven has studied family incidence with special reference to immunity.
Thomas Sydenham, speaking of the epidemic of 1675, says that: “No one escaped them whatever might be his age or temperament, and they ran through whole families at once.”
According to Waldschmidt, during the epidemic of 1712, in Kiel, ten or more persons were frequently taken ill in one house.
In 1732, Huxam tells us that, “not a house was free from it, the beggar’s hut and the nobleman’s palace were alike subject to its attack, scarce a person escaping either in town or country, old and young, strong and infirm, shared the same fate.”
Metzger says that the influenza was so universal in March, 1782, that in very many houses all of the inmates were attacked. On the other hand, Mertens did not believe the influenza a contagion during the same epidemic for the reason that according to his observations now only one, and again all, of the members of a family, were stricken.
In 1833, in Königsberg, according to Hufeland, parents, children, and servants were frequently smitten with the disease at the same time, so that strange help had to be obtained for the family.
Parkes taught that, “Persons in overcrowded habitations have, particularly in some epidemics, especially suffered, and several instances are on record of a large school or a barrack for soldiers being first attacked, and of the disease prevailing there for some days before it began to prevail in the town around. Sometimes, on the other hand, schools and prisons have escaped. A low, damp, ill-ventilated and unhealthy situation appears to predispose to it, and in some instances, in hospital patients, it has assumed a malignant character. In other cases again, hospital patients have escaped; for example, the old people in the Salpêtrière in 1837, when the younger attendants were attacked.”
Effect of overcrowding.—The family or household forms a social unit in which human intercourse is very close, and in which the opportunities for contact infection either direct or indirect are manifold. In addition to all of the opportunities which each individual has for contracting the disease outside of the family every case in the family exposes every other member many times during the day. One of the first questions arising in a study of the disease in the family is, therefore, whether the size of the family in and of itself exerts any predisposing influence on the total incidence in any one family. Are large families more likely to have a greater percentage of cases than small families? We have endeavored to answer this question by grouping together all families containing only one individual, all of those with two, three, four, etc., and determining the percentage of individuals contracting influenza in each of the groups. The standard for comparison is the percentage of the total 10,000 who contracted the disease in either year, or in both. 19.71 per cent. of all persons canvassed contracted influenza in 1918–19. Reference to Table IV shows that of persons living in families of one, 17.95 per cent. developed the disease; of those in families of two, 18.46 per cent.; in families of three, 19.96 per cent.; in families of four, 20.10 per cent.; and in families of from five to seven, between 22 and 23 per cent. Families of over seven all showed lower, but varying incidence of the disease. As is seen by the table, they comprise only a small number of families.
| TABLE IV. | ||||||||
|---|---|---|---|---|---|---|---|---|
| The incidence of influenza in families of different sizes. | ||||||||
| (Influence of size of family). | ||||||||
| No. of individuals in family. | No. of such families. | Total No. of individuals included in all such families. | Number of these individuals who developed influenza. | |||||
| 1918. | 1920. | Total. | ||||||
| No. | Per cent. | No. | Per cent. | No. | Per cent. | |||
| 1 | 39 | 39 | 7 | 17.95 | 3 | 7.69 | 10 | 24.42 |
| 2 | 260 | 520 | 96 | 18.46 | 55 | 10.58 | 151 | 29.04 |
| 3 | 359 | 1077 | 215 | 19.96 | 128 | 11.88 | 343 | 31.85 |
| 4 | 396 | 1584 | 319 | 20.10 | 169 | 10.67 | 488 | 30.81 |
| 5 | 375 | 1875 | 423 | 22.56 | 203 | 10.83 | 626 | 33.39 |
| 6 | 264 | 1584 | 361 | 22.79 | 151 | 9.53 | 512 | 32.32 |
| 7 | 179 | 1253 | 279 | 22.27 | 109 | 8.70 | 388 | 30.96 |
| 8 | 103 | 824 | 156 | 18.93 | 55 | 6.67 | 211 | 25.61 |
| 9 | 57 | 513 | 85 | 16.57 | 21 | 4.09 | 106 | 20.66 |
| 10 | 28 | 280 | 40 | 14.14 | 26 | 9.29 | 66 | 23.57 |
| 11 | 15 | 165 | 10 | 6.06 | 7 | 4.24 | 17 | 10.30 |
| 12 | 4 | 48 | 0 | 0.0 | 5 | 10.42 | 5 | 10.42 |
| 13 | 2 | 26 | 5 | 19.23 | 3 | 11.54 | 8 | 30.77 |
| 14 | 1 | 14 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 |
In 1920, 9.55 per cent. of the entire canvassed population contracted the disease. The table shows that 7.69 per cent. of all individuals in families of one contracted influenza, and between 10 and 12 per cent. in families of from two to five individuals. Above the family of five the incidence rates again are lower and varying within wide limits. The last column shows the percentage of individuals by size of family contracting the disease in either or both epidemics.