Part 24

H. F. Vaughan reached comparable results for the 1920 epidemic in Detroit. During the first few weeks the age groups from 20 to 29 showed a relatively much more frequent influenza incidence than did children up to ten years. In later weeks of the epidemic there was a relative increase in the incidence among children and decrease among young adults. He concluded that the disease first attacks the young adult and from this group it extends into the home.

In the Local Government Board Report for 1891, H. H. Murphy distinguishes three groups or ways in which the disease may be brought into the family. The examples will be found to be characteristic for any epidemic and for any country:

_Group A._—Cases of single exposure.

“Household 1.—Mr. Q. goes to London daily. Was ill with influenza on December 25th. No other case in this house till January 15th.

“Household 2.—Mrs. A. called on Mr. Q. on December 31st, and had a few minutes’ conversation with him. She was taken ill on January 3d. There was a Christmas family gathering at this house, and this is how the other members were affected: Mr. B., January 6th; Miss C., Mrs. D., and Master D., January 8th; Mr. J., January 10th; Mr. H., January 11th.

CHART XXVII.

“Household 3.—Miss M. went to a party January 3d. She had a few minutes’ conversation with a young lady who said she was suffering from influenza. Miss M. had a characteristic attack on the 6th of January.

“Household 4.—Mr. G. goes to London daily; taken ill January 5th. Mrs. N. visited him for a short time on January 5th, and was taken ill January 10th.”

_Group B._—Where disease was brought from a distance into a previously healthy household.

“Household 8.—Mrs. R. G., living in the north of London, came here on a visit December 17th. On the 19th she was taken ill with influenza, the first case that I knew of in this neighborhood. Mr. C. G., on the 23d, servant on the 26th, Mrs. G. 31st, and Mr. G. January 9th.

“Household 9.—Mr. I. lives at his business place in London, taken ill December 20th with influenza. His family reside here. Boy C. visited his father for a few days, and came back ill on January 4th. The other members of the family were attacked as follows: Baby, 8th; Mrs. and boy, 12th; boy, 18th, girl, 22d; girl 25th.

“Household 10.—Master K. stayed a few days with some friends in London. They had been ill with influenza. Returning home on December 31st he was taken ill. Four brothers and sisters ill on the 2d January, Mr. K. on 3d, child and two servants on the 5th, Mrs. K. on the 7th.”

_Group C._—Where the source of infection could not be determined or was local.

“Household 28.—Mrs. D. (who thinks she got it shopping) was taken ill 2d January, her daughter on the 5th, and Mr. D. on 6th.

“Household 29.—Mrs. L. (who thinks she got it shopping), aged 80, had influenza badly in 1847; similar symptoms, but much milder, on January 6, 1890; Miss L. was attacked on the 10th, and servant on the 17th.

_Note._—A former attack did not confer immunity after forty-three years.

“Household 30.—Mrs. B. (who thinks she got it out at work) taken ill 9th January, and her child on the 11th.”

In Murphy’s complete list, one of the most frequent remarks is, Mr. Blank goes to London daily. Or, Miss Blank, absent on a visit, was taken ill with influenza and returned home.

Again, in 1890, Dr. Bruce Low studied the development of influenza at East Keal, a town of 300 inhabitants. We quote in part his description:

“The following is believed to have been the commencement of the outbreak, and for these facts I am indebted to Dr. Francis Walker, Medical Officer of Health, Spilsby, R. S. D. Mrs. N., residing at East Keal Hall, went to London (Forest Hill) on a visit on November 11th. She visited Barnum’s Show on November 13th. She became ill on the night of the 14th. Her symptoms were those of a cold, attended with sore throat. No one else so far as she knew was ill in this way in the house before her. She left Forest Hill on November 16th, still feeling very unwell, and went to stay with friends at Kensington. She was too ill to return home till November 23d, at which time she was still feeling very weak. She heard from Forest Hill that, directly after she left one of the inmates of the house where she had been visiting fell ill with symptoms similar to her own. Within a few days, probably about the 27th of November (the exact date is not fixed), of her return home, her son, aged four, became unwell with what appeared to be an ordinary cold, but the child had epistaxis; he soon recovered, but during the next fortnight the four servants in the house were ill with what were said to be ‘colds,’ one of them also had epistaxis. On January 2d another son, aged six, was ill with ‘cold’ for a few days; he went out and had a relapse, which compelled him to stay in the house for another week.

“On January 3d, Mrs. N. again fell ill with ‘a bad cold,’ attended with headache, backache and epistaxis. She was in bed two days and felt miserable and prostrate for more than a week after. On January 5th, Mr. N., her husband, had headache, backache, and general soreness ‘all over.’ On January 10th, the boy, aged four, who was first attacked after his mother’s return from London, again became ill, his symptoms being the same as before. The only other remaining member of the family who had managed to escape an attack of ‘cold’ up to this date, was said to have felt ill the day the boy had his second attack; but the illness of this individual was slight, and only caused suffering for one night. Thus between the return of the mother on November 23d and January 10th all the inmates of this house, nine in number, had an attack of illness, evidently of the same nature. A boy who works in Mr. N.’s yard was taken ill with influenza about the end of November. He lives in the village. After his illness his four brothers also were ill. Dr. Walker says that ‘about the end of November’ cases of like illness were beginning to crop up in East Keal. Mrs. W., the wife of the village grocer and baker, who waited on customers in the shop and never left the shop or house, was taken ill on the afternoon of November 30th. Next morning, December 1st, her husband and six children were all attacked in the same way with what is now recognized to have been marked influenza. The only inmate of the house who escaped was a youth employed to deliver bread and groceries in a cart in the neighboring village.”

Leichtenstern relates that a physician traveling from Berlin on the 10th of December became sick in his home town, Elgesburg, on the 8th of December, but he made several visits and a few days later those people seen by him fell sick, while otherwise there were no cases of influenza in the town or its neighborhood. These cases would probably have fallen in Group C., of Murphy’s classification.

_Intimacy of family contact._—We have been able to discover in a representative number of families in which influenza has occurred, not only what individuals slept in the various rooms of the household, but also what individuals slept in the same bed with influenza cases. We can, therefore, study for the 1920 epidemic three degrees of contact; contact by sleeping with a case of influenza; by sleeping in the same room but a different bed; and general contact by being in the family, but sleeping in another room. For brevity we designate these, “_sleeping_,” “_room_” and “_family_” _contact_. We have established similar information for 1918, after eliminating families in which deaths or births or other additions or losses had occurred during or subsequent to the 1918 pandemic, in which there has been a change of address, in which the cases are so widely separated that we have designated them _unrelated_, and finally, those families in which the information has been insufficient. With the remaining we have assumed that the distribution within the household has been the same in both epidemics. Statistics are available on 1,734 individuals who in 1918 were exposed to a prior case in the family. Of these, 462 developed influenza and 1,272 did not. 26.6 per cent. of exposed individuals in families contracted influenza, without respect to the degree of exposure.

═════════════════╤═════════════════╤═════════════════╤═════════════════ Intimacy of │ Number so │Number infected. │ Per cent. contact. │ exposed. │ │ infected. ─────────────────┼─────────────────┼─────────────────┼───────────────── “Sleeping” │ 360│ 166│ 45.2 “Room” │ 303│ 59│ 19.5 “Family” │ 1,064│ 273│ 22.3 ─────────────────┴─────────────────┴─────────────────┴─────────────────

45.2 per cent. of individuals sleeping with cases of influenza in 1918 contracted the disease; 19.5 per cent. of those sleeping in the same room, but different beds did so; 22.3 per cent. of those living in the same family, but sleeping in other rooms contracted the disease.

_Sleeping contact is more productive of influenza than are the less intimate forms._

Throughout this study the fact that there are multiple possible sources of infection both outside and often within the family complicates the picture.

The results for 1920 are similar. Here, 30.0 per cent. of all individuals sleeping with cases of influenza contracted the disease, 17.7 per cent. of room exposures contracted it, while but 11.5 per cent. of family exposures were attacked.

Four hundred and sixty-three or 29.1 per cent. of the total of 2,193 individuals exposed in 1920 had had the disease in the 1918 pandemic. Did they show by reason of any immunity a lower attack rate for the same degree of exposure than other individuals in 1920?

═══════════════════════╤═══════════════════════╤═══════════════════════ │ Per cent. of exposed │Per cent. of those who Type of exposure in │individuals who had had│had not had a previous 1920. │ influenza in 1918–19 │ attack, and who on │ and who contracted it │ exposure contracted │ again, per cent. │ influenza, per cent. ───────────────────────┼───────────────────────┼─────────────────────── “Sleeping” │ 27.0│ 31.0 “Room” │ 18.3│ 17.6 “Family” │ 12.0│ 11.2 ───────────────────────┴───────────────────────┴───────────────────────

_On the whole there is no evidence of protection afforded by a previous attack._—Individuals who had had the disease before succumbed to a second attack in the same proportion as those who had not previously had influenza.

_Recurrent cases._—In certain families there were individuals who had had influenza during both the 1918 and 1920 epidemics. Were these recurrent cases the first ones to occur in the family, or did they, as a rule, follow other cases in the same household? We have records of 236 recurrent cases in which we know the order of occurrence of the various cases in the family. Out of this total number 57 were the initial cases in the household. One hundred and nineteen were the only cases occurring in the family. Therefore 176 or 74 per cent. of the total number of recurrent cases were either the first or the only cases in the family. Sixteen recurrent cases followed between other cases and 44 occurred as the last of a series of two or more in the household.

SECTION V.

IMMUNITY.

Opinions of all observers who have studied in detail the question of immunity in influenza are remarkedly in accord. The conclusions reached by Parkes in 1876 are valid today, and form as excellent an abstract of our present knowledge as any produced since his time. “There is some discrepancy of evidence, but, on the whole, it seems clear that, while persons seldom have a second attack in the same epidemic (though even this may occur), an attack in one does not protect against a subsequent epidemic. Indeed, it has been supposed rather to render the body more liable.”

In 1890, Abbott wrote: “There is but little if any evidence in support of the protective power of one attack to confer immunity against a second; and hence adults are not exempt, as they usually are in epidemics of scarlet fever or other exanthemata; so that the proportion of adults to children attacked in an epidemic is necessarily greater than that which is observed in epidemics of other infectious diseases.”

Parsons made somewhat similar observations: “One attack of influenza does not seem to be protective against another; the disease in this respect resembling diphtheria, erysipelas, and cholera rather than smallpox, measles, or whooping cough. The duration of the epidemic in a locality is so short that it is difficult to distinguish between second attacks properly so-called, and relapses, which are frequent enough. A case is recorded in the ‘British Medical Journal’ of February 15, 1890, in which a patient who had suffered from influenza in France in December, 1889, had another attack in England in January, 1890. It was noticed in 1837 that many persons suffered from influenza who had had the disease during the previous epidemic in 1834. The shortness of the interval between these two epidemics, as compared with that between 1848 and 1889, seems to show that the periodical return of the disease in an epidemic form does not depend upon the accumulation in the interval of susceptible individuals unprotected against the disease by a previous attack. If one attack afforded protection against another a large proportion of the population in 1837 must have been protected, yet an epidemic occurred, and on the other hand for many years before 1889 a large majority of the population must have been unprotected by a previous attack, yet the epidemic did not recur.

“The persons now living who passed through the disease in 1847 are of course comparatively few, but such persons have not been exempt from the present epidemic.

“I should be inclined to attribute the short duration of the influenza epidemic in a locality to the establishment of a tolerance for the specific poison among the persons exposed to it, similar to the tolerance for dust possessed by workmen in rag factories, as mentioned, but which is soon lost on their ceasing to be exposed to it, rather than to a true immunity being established.

“Relapses in influenza are of frequent occurrence; they occurred in 9.2 per cent. of the cases at the Morningside Asylum, Edinburgh, and in some cases indeed a second relapse has been recorded. The time at which the relapse occurs is usually from a week to a fortnight after the primary attack, and it can often be distinctly traced to an exposure to cold, or return to work before complete recovery. The symptoms of the relapse are similar to those of the primary attack, except that they are commonly more severe.”

In his report of 1893, Parsons goes into the subject of recurrent attacks in individuals in greater detail. He quotes several communications received from various physicians and health officers. These opinions differ, some believing that the disease predisposes to another attack; others, that there is no effect on the incidence in recurring epidemics; and still others believing that there is a small amount of acquired immunity. The communications are not based upon statistical evidence. He does find, however, an opportunity for statistical study in the industrial schools at Swinton near Manchester: “These schools were severely affected in March, 1890, 171 out of 589 children having suffered, or 29 per cent. In the first epidemic of 1891 they were again affected, but to a less extent, only 35 cases occurring. At that time there were in the schools 449 children who had been there at the time of the former epidemic. Of these 150 had had influenza in 1890 and 4 of them had it again, or 2.6 per cent.; 299 had escaped influenza in 1890 and 17 of these had it now, or 5.7 per cent. Thus, so far as these figures go, an attack of influenza confers a degree of protection which after the lapse of a year diminishes by one-half the liability to contract the disease.”

Leichtenstern, like Parsons, recognizes the importance of distinguishing between relapses and recurrent cases. Relapses in influenza are not common. They usually occur after the patient is up, and about when he is ready to leave the house. These are not recurrent cases, but in the epidemics in the years following 1889 there were plenty of well substantiated cases of recurrent typical influenza in the same individual and some times even in entire families. During the 1889 epidemic, as during the 1918 epidemic it has been suggested by various observers that the apparent immunity among the very old was due to immunity developed as the result of previous epidemics, such as that of 1837, 1847 and 1857. Leichtenstern has collected the statistics from five different hospitals in which 8, 32, 35, 24, and 24 per cent. of individuals attacked in 1891–92 had already had the disease in 1889.

Allbutt in 1905 remarked that whereas he had previously believed that immunity to influenza usually persists as long as six months, many cases had recently been brought to his notice where such an interval seemed improbable, where the succeeding attack was probably not a relapse but a new infection. He has seen two attacks apparently separate occurring in the same individual within two months. In the same year Moore wrote that influenza shows a decided tendency to relapse, a feature to which the indirect fatality of the disease is in great measure due. “So far from establishing immunity, an attack of this malady seems to render an individual more liable to contract the disease upon any future exposure to its contagion.”

Again West, in the same year wrote, “From our present experience we must conclude that influenza is infectious in a very high degree indeed, and that the protection afforded by an attack is imperfect, or of very short duration. Indeed, one attack seems actually to predispose, after a time to another, or, to put it differently, that the positive phase of protection is followed by a negative phase, in which the individual seems rather more than less liable to succumb to infection if exposed to it. It seems more likely that an individual may never have influenza at all than that, having had it once, he should never have it again. Some, indeed, seem to offer so little resistance that they develop it regularly once or twice a year.”

We have previously shown that the relatively low morbidity among the older age groups in 1918 is not satisfactorily explained by an immunity lasting over from the epidemic of 1889–93. If such were the case the change in mortality rate in large groups of individuals would occur at the age of 30.

During the autumn of 1918 many observations were made, particularly in the armies, of light incidence in those groups or communities that had had the disease in mild form in the spring of the same year.

Parsons quotes many similar observations for the period 1890–1893.

V. C. Vaughan relates that at Camp Shelby, Mississippi, “there was in April a division of troops numbering about 26,000. An epidemic of mild influenza struck this camp in April, 1918, and within ten days there were about 2,000 cases. This included not only those who were sent to the hospitals, but also those who were cared for in barracks.

“This was the only division that remained in this country without change of station from April until the fall of 1918.

“During the summer this camp received 20,000 recruits. In October, 1918, the virulent form of influenza struck this camp. It confined itself almost exclusively to the recruits of the summer and scarcely touched the men who had lived through the epidemic of April. Not only the 2,000 who had the disease in April, but the 24,000 who apparently were not affected escaped the fall epidemic. It appears from this that the mild form of influenza of April gave a marked degree of immunity against the virulent form in October. There is another observation which points the same way. Looking over the statistics of the fall epidemic in cities in the United States we find that certain cities had a low death rate, while others had a relatively high rate. Among those cities which had a low death rate we will mention Atlanta, Ga.; Kansas City, Mo.; Detroit, Mich., and Columbus, Ohio. Going to the spring records of these cities we find that in all of them in March and April of 1918 there was an unusually high death rate from pneumonia and undoubtedly in these cities at that time there was a relatively mild epidemic of influenza. In this way I am inclined to account for the relatively low death rate in these cities in the fall of 1918. I make no claim that this and other instances of a similar kind prove that the mild and virulent forms of influenza are manifestations of the same disease, but I do hold that the evidence points that way.”

Lemierre and Raymond report the following observation in favor of the development of a certain degree of immunity in the French troops in April, 1918. After an intervening period of quiescence there was a manifest recrudescence at the end of August. Many military formations were attacked during both periods. This was true especially in three groups of an artillery regiment under their observation. In the first of these groups there were three cases in April, while 114 men were attacked in August. In the third group there were 100 cases in April and only 3 in August. In the second group there were 20 cases in April and 59 in August. Their report does not state the total number of individuals in each of the three groups.

Joltrain and Baufle discuss the flaring up of the epidemic in October, and relate that a troop of soldiers from Indo-China nearly all had the disease lightly in the spring, but when the disease appeared again it spared this troop completely, while troops and civilians around developed it in a severe form.

Gibbon writes: “During the last three waves of the epidemic I had to deal with the sick of 2,000 troops, and during this time we treated in hospital over 400 cases. No cases admitted in June, July or August were re-admitted in October, November, or December, and no cases admitted in either of these two periods were re-admitted in February this year. Unfortunately I am unable to trace the cases into March as the troops were changed.”

Dopter reports recurrent epidemics of influenza in a French Army Division in 1918. The division, of which he was surgeon, was one of the first to contract la grippe at the time of its first appearance in the zone of the armies at the end of April, 1918. At this time nearly the entire body of infantry troops was attacked. The disease was mild, and without complications. The regiment of artillery escaped nearly entirely. This epidemic subsided very rapidly, and by the end of May it had entirely disappeared. Early in August a group of heavy artillery was attached to the division, bringing influenza with it. Then a few cases appeared in the regiment of light artillery which had hitherto escaped. By the end of August all three groups of this regiment had been attacked. In this second epidemic the men who had come through the first unattacked were very severely ill in the second.