Manner of Spread.
More characteristic and more important from an epidemiologic standpoint than the symptomatology in general, as we have discussed it, is the mode of development of the epidemic as a whole.
Human intercourse.—Before the days of bacteriology the contagiousness of the disease was little discussed. Its infectiveness was in fact not universally established until the epidemic of 1889–1890. One of the first writers who attempted to see in the influenza a contagious disease was Ch. Calenus who wrote in 1579: “Contagiosum dico morbum, quia etsi quidem ab occulta quadam coeli influentia, principaliter eum profisci haud dubium est ... eo in loco quo jam grassabatur inter homines citius eos invadabat, qui cum affectis frequenter conversabantur, quam eos, qui a consuetudine affectorum studiose abstinebant.” This keen observer saw that those who carelessly exposed themselves to close contact with cases of influenza were more likely to develop the disease than those who protected themselves in every way possible. The “contagious” school first developed in England, where Haygarth, Hamilton, Gray, Hull, Duggard, Bardsley, and others, in 1775–1803 described the disease as being not in the air, but in a specific contagion. Others who considered influenza a contagious disease were Simonin, Lombard, Petit de Corbeil (1837), Blanc (1860), and Bertholle (1876).
Watson (1847) quotes Cullen as saying that this species of catarrh proceeds from contagion. He, himself, is not convinced of this fact. He says the visitation is too sudden and too widely spread to be capable of explanation in that way. “There are facts in the history of influenza which furnish a strong presumption that the exciting cause of the disorder is material, not a mere quality of the atmosphere; and that it is at least portable. The instances are very numerous, too numerous to be attributed to mere chance, in which the complaint has first broken out in those particular houses of a town at which travelers have recently arrived from infected places.... What I wish to point out now is the fact that the influenza pervades large tracts of country in a manner much too sudden and simultaneous to be consistent with the notion that its prevalence depends exclusively upon any contagious properties that it may possess.”
Parkes, writing in Reynolds’ System of Medicine in 1876, views the subject more as we see it today: “The rapidity of the spread would seem at once to negative any connection between human intercourse and the propagation of the disease; yet there is some affirmative evidence. It does not appear to follow the great lines of commerce; but when it has entered towns and villages in which the investigation can be carried on, it is curious how frequently the first cases have been introduced, and how often the townspeople nearest the invalids have been first affected. In this country especially, Haygarth in 1775 and 1782, and Falconer in 1802, collected so many instances of this that they became convinced that its propagation was due entirely to human intercourse. So also, when it passes through a house, it occasionally attacks one person after another. But if it is introduced in this way it afterwards develops with marvelous rapidity, for we cannot discredit the accounts of many thousands of persons being attacked within a day or two, which is quite different from the comparatively slow spread of the contagious diseases. This sudden invasion of a community makes it, to many persons, appear highly improbable that any effluvia passing off from the sick should thus so rapidly contaminate the atmosphere of a whole town.
“Still, we must remember how singularly, of late years, the knowledge of the introduction of cholera by persons coming from infected districts has increased, and how very striking are the instances of this kind already recorded in several works on influenza.
“In some cases, again, isolation or seclusion of a community, as in prisons, has given immunity; or at least that community has not been attacked.”
The great rapidity of spread has caused even in 1918 some temporary doubt as to the contagiousness of the disease. Thus, Zinsser wrote:
“The opinion of direct and indirect transmission from man to man is also well supported by a detailed study of the epidemiology of individual outbreaks. In our own experience with epidemics such as those at Chaumont, Baccarat and other places, the suddenness with which the malady attacked large numbers of people at almost one and the same time, caused me at first to be exceedingly skeptical of accepting transmission by contact as the only means of conveyance. We considered food and insect transmission as possibilities, and tried our best to find grounds for involving such agencies. But in every case we were forced to return to the conclusion that direct and indirect contact between men came nearest to doing justice to all observed facts.”
There have been many examples reported from personal experience to show that influenza is transmitted from man to man. Two objections, however, have had to be met, before this view was generally accepted. First, it has been claimed by some that the disease spread more rapidly from an assumed focus than individuals could travel, and second, that instances were on record of cases occurring spontaneously in isolated communities. Yet a third argument formerly raised against the contagious character of the disease was the claim that it broke out in mass attacks, that large numbers became ill on the same day without the occurrence of isolated antecedent cases. The splendid work of epidemiologists following the 1889 epidemic appears to have answered all of these objections. Many, such as Leichtenstern, have gone into great detail on this subject. In fact, at that time this was the question of greatest importance. Today we assume the correctness of the hypothesis, and pass on to consideration of other subjects of more recent development. We will, therefore, review very hurriedly some of the evidence quoted to prove that influenza is transmitted only from man to man and only by human intercourse.
Isolated places.—Has it ever been shown that individuals completely isolated from communication with communities where influenza is present have, during an epidemic, developed the disease? Leichtenstern, after a comprehensive review, concludes as follows: “We have not a single example on record where influenza has attacked individuals in completely isolated localities, as on mountain tops and mountain passes. Study of this has been undertaken in Switzerland by F. Schmid. The same has been true of ships at sea, as has been shown chiefly from the English Marine Reports. There have been reports of influenza occurring in mid-ocean and particularly in the earlier epidemics, but the information has been insufficient.”
Parkes at even an earlier period observed: “I cannot but consider that we require better evidence of ships being attacked in mid-ocean. In some of the quoted instances the ships had been at a port either known to be infected or in which influenza was really present, although it had not become epidemic. As we are ignorant of the exact period of incubation some men may have been infected before sailing.”
Critical investigation into stories of spontaneous infection in isolated localities such as ships at sea and island lighthouses will quite invariably demonstrate that these popular reports have been distortions of the actual facts. One or two examples will suffice. Abbott records an example: “An impression having gained some credence that influenza had appeared on board the squadron of naval vessels which sailed from Boston in December, 1889, while on their course across the Atlantic and before their arrival in Europe, a letter was addressed by the writer to the Bureau of Medicine and Surgery of the United States Navy for information upon this point, to which a reply was received, as follows:
“The ‘Chicago,’ ‘Boston,’ ‘Atlanta’ and ‘Yorktown’ left Boston December 7, 1889, for Lisbon, Portugal. The first three arrived at Lisbon on December 21st without having touched at any port en route. The ‘Yorktown’ arrived at that port December 23d, having, stopped about twenty-four hours at Fayal, Azores.... Influenza first appeared on the ‘Chicago’ December 23d, on the ‘Boston’ December 28th, on the ‘Atlanta’ December 30th and on the ‘Yorktown’ December 28th.
“Influenza was prevailing in Lisbon at the date of arrival of the squadron.”
In March, 1920, the author was notified of a somewhat similar story which he undertook to trace. The results show well the inaccuracy of verbal transmission through several individuals. A letter was first sent to the Quarantine Officer at Portland, Maine: “It has been reported to us that in a lighthouse just outside of Portland, Maine, there has been a rather interesting prank played by influenza. We are told that three men and one woman live in the lighthouse; that during the 1918 influenza epidemic the woman contracted the disease while none of the men became sick, and that in the present epidemic all three of the men became sick with the disease and the woman remained well. It was claimed that they had had no communication with the mainland for some time before the men became ill,” etc.
The reply was as follows: “I have inquired of the Light House Inspector’s office in Portland and they know of no stations to which the terms of your inquiry would apply.
“At the Boon Island station, there are three keepers with families. At the Half Way Rock station, there are three keepers but no woman. The Inspector does not seem to know of any station where there are three men and one woman.”
A second letter, sent to the Inspector of Lighthouses at Portland brought corroborative information:
“The Boon Island Light Station was stricken by this epidemic in the following manner: The keeper, his wife and five children were all stricken, the keeper himself having had the hardest battle, having apparently been subject to same while ashore in Portsmouth, N. H. after provisions, supplies, etc. The 2d assistant’s wife and two children were also stricken, but the 2d assistant, himself, and the 1st assistant keeper did not contract the malady in spite of the fact that they were all confined on a small island working together at the station.
“During the year 1920 none of the keepers or their families, consisting of thirteen in number, were affected. The Halfway Rock Light Station where three keepers are employed did not contract this malady either in the years 1918 or 1920.
“For your information I might add that during the inspection trip in the months of January, February and March, 1920, all of the light stations in this district were visited, and it was found that they were all enjoying good health and had not been visited by the epidemic, with the possible exception of three stations which are located either on the mainland or close to where the keeper or his family were able to visit the nearby cities or towns.”
Although it has not been shown that completely isolated places have been visited by the disease, there is abundant evidence that such places have remained influenza free as long as the isolation has remained complete. Islands and lighthouses, which have not been in communication with the mainland, individuals living isolated on mountain tops, and ships at sea remained free from influenza even in the presence of a pandemic, as long as they did not come into communication with individuals sick with the disease. The following places remained free from influenza throughout the 1889 epidemic: the Isle of Man, several of the islands of the West Indies, particularly the Bahamas, Granada and St. Lucia, also the British Honduras, British Guiana, and the Seychelle Islands.
Even in 1918, when the paths of commerce reached nearly every portion of the world, we have examples of relative immunity of isolated places. Thus we know that the Esquimaux were attacked late in the course of the pandemic, and we have the statement of Barthélemy who traveled in 1919 to some of the oasis towns of the Sahara Desert, and there discovered that there had not only been no influenza up to that time, but also that they had not even heard of the pandemic.
Another type of isolated place is the closed institution. As early as 1709, Lancisi remarked that the prisons of the Inquisition in Rome remained free from influenza. Twenty-one prisons in Germany in 1889–90 remained entirely free from the disease. This was true of 39 prisons in England, some of which were in cities where the epidemic was most extensive. Linroth, who observed this same phenomenon in Sweden, makes the wise remark that, “the influenza conquers more easily the space of 500 to 1,000 kilometers than it does the small barrier made by a prison wall.” A convent in Charlottenburg housing one hundred women remained entirely free during the 1889–90 epidemic.
As a rule institutions of this sort have been unable to maintain a complete quarantine throughout the period of an epidemic, and the relative immunity has been demonstrated more in late invasions, at a time when the restrictions have become somewhat lax. Thus, in 1918, Winslow and Rogers, report that in an orphan asylum in New Haven, Connecticut, which had completely escaped during the month of October when the epidemic was at its height, one of the Sisters and the priest in charge came down with influenza about December 15th. By the 27th of December 127 cases had occurred in the institution within twenty-four hours, and by January 7th there had been 424 cases, with seven deaths out of a total population of 464. The probable source of the sudden outbreak of December 27th seems to have been the Sister first affected who, when convalescent, resumed her duties in the kitchen, which included the inspection and handling of the milk given out to the children.
Crowd gatherings.—Yet another phenomenon which would lead us to conclude that human intercourse is the most potent factor in the transmission of influenza is the fact that there is frequently a high increase in the influenza rate following crowd gatherings. Parkes observed long ago that persons in overcrowded habitations, particularly in some epidemics, suffered especially, and several instances are on record of a large school or a barracks being first attacked and the disease prevailing there for some days, before it became prevalent in the towns around.
In England, the weekly market played an important role in the spread of the disease in 1889. One frequently saw such reports as that: “The first case of influenza was a man who went to London daily.” Or, “All the earliest cases were men going to London daily, while their wives and families were later affected.”
In the epidemics at San Quentin Prison, it was noted that apices of incidence usually occurred on Tuesday and Wednesday. During the first epidemic it was these days of the second and third weeks. Stanley sees a direct connection between this fact and the fact that every Sunday morning large groups of the men were crowded together in a comparatively small auditorium where they saw moving pictures. On Sunday, October 20th, they sought to eliminate this source of spread by having a band concert in the open air, but the prisoners crowded around the band and were loud in their cheers, and on the following day there was a large increase in hospital admissions.
On November 24th after the second epidemic had apparently ceased the picture shows were again started after having been closed for over six weeks. The following Tuesday and Wednesday twenty-four well defined new cases were admitted to the hospital. On Thanksgiving Day there was a field meet between the various departments of the prison. About 200 prisoners took active part, while 1,600 prisoners were spectators. The meet was held in the open air, but the prisoners were closely packed and they cheered and yelled. For the three days following this celebration there were 9, 5 and 8 patients admitted respectively.
In discussing the recrudescence of influenza in Boston in November and December, Woodward remarks as follows:
“Whether or not it may be more than a succession of coincidences it is certainly of interest to note that the November outbreak of influenza showed itself three days after the Peace Day celebration on November 12th, when the streets, eating places and public conveyances were jammed with crowds; that the December epidemic began to manifest itself after the Thanksgiving holiday, with its family re-unions and visiting; and that reported cases mounted rapidly during the period of Christmas shopping, reaching a maximum a week after the holiday.” That this may have been a coincidence is indicated by the fact that, according to reports by Pearl and others this was not consistently true in other large cities.
Dr. Meredith Davies records the case of a hostel in Wales accommodating 200 students. Infection was introduced on October 19th on the occasion of a dance attended by some students from an infected institution in the neighborhood. Four cases occurred on the 20th and within the short space of five days seventy-nine students out of the 200 were attacked.
Parsons found numerous similar examples in the epidemic of 1889. In 1918 it was frequently observed that among American Soldiers in France, those troops quartered in barracks suffered a much more rapid spread of the disease than those billetted out among the houses of the towns.
Mass attack.—Another argument formerly raised against the contagious character was the claim that it broke out in mass attack, and large numbers became ill on the same day without the occurrence of isolated antecedent cases. The first cases of such epidemic diseases as the plague and small pox became a matter of record because of the accompanying high mortality, while in influenza, with its relatively low death rate the record usually begins only after a comparatively large mass of individuals have been attacked.
Watson in 1847 observed as follows: “Although the general descent of the malady is, as I have said, very sudden and diffused, scattered cases of it, like the first droppings of a thunder shower, have usually been remembered as having preceded it. The disorder is most violent at the commencement of the visitation; then its severity abates; and the epidemic is mostly over in about six weeks. Yet the morbific influence would seem to have a longer duration. In a given place nearly all the inhabitants who are susceptible of the distemper suffer it within that period, or become proof against its power. But strangers, who, after that period, arrive from uninfected places have not, apparently, the same immunity.”
Parkes in 1876 observed that, “When the disease enters a town it has occasionally attacked numbers of the inhabitants almost simultaneously. But more frequently its course is somewhat slower; it attacks a few families first and then in a few days rapidly spreads; the accounts of thousands of persons being at once attacked at the onset of the disease are chiefly taken from the older records, in which the suddenness of the outbreak is exaggerated. Frequently, perhaps always, in a great city the outbreak is made up by a number of localized attacks, certain streets or districts being more affected than others, or being for a time solely affected, and in this way it successively passes to different parts of the city. It has generally occurred in a great city before appearing in the smaller towns and villages round it and sometimes these towns, though in the neighborhood, have not been invaded for some weeks.
“In some cases and perhaps a large number, it breaks out after persons ill with influenza have arrived from infected places.
“The decline in any great town is less rapid than its rise, and usually occupies from four to six weeks, or sometimes longer.”
Detailed studies of the Munich epidemic of 1889 and numerous similar studies of the recent epidemic, which will be referred to later, have shown a period of two or three weeks of steadily increasing numbers of cases before the height of the epidemic was reached.
Droplet infection and spread through inanimate objects.—The actual mode of spread of the virus of influenza from one individual to another is unknown. The more generally accepted explanation is that the infecting agent leaves the body through the respiratory tract, usually in the spray of coughing or talking; contagion is by droplet infection, as is sometimes the case in other respiratory infections. Thorne and others have called attention to the capillary congestion of the conjunctivae very early in the disease. They suggest that possibly the mucous membrane of the eye is the site of infection.
There has recently been considerable discussion concerning the spread of influenza through inanimate objects.
Leichtenstern reviews the reports of 1889–93 in which influenza was supposed to have been transmitted through wares, merchandise and other inanimate objects. He concluded that the evidence in all of the cases cited was insufficient for conclusive proof. Such an example was the supposed importation of the disease in goods sent from Russia to the Grands Magazins du Louvre at Paris. In one day 100 people became ill and in a few more 500 were sick with influenza. The explanation was that the germs had been imported in goods sent from Russia to the store. Detailed investigation showed that this could not have been the case because no goods had been received from Russia for a period of three years. Another example is that of one of the two winter caretakers at the St. Gothard Hospice. One of the two men went down into the valley where he purchased supplies. Ten days after his return the man who had remained in the Hospice fell ill with influenza while his comrade remained well. It was stated that influenza was introduced into Basel by goods shipped to that place from the Magazins du Louvre in Paris. The first case occurred in a man who had been working at unpacking these goods.
Lynch and Cumming believe that droplet infection plays but a minor role in the spread of sputum-borne diseases, but that insanitary methods of washing dishes and eating utensils was the chief cause for the high rates of “sputum-borne” infections both in army and civilian life in 1918. They found that among 31,000 troops eating from tableware which was cleaned by kitchen police, the influenza rate was 51 per 1,000, while among 35,000 eating from mess kits which each individual washed himself the rate was 252 per 1,000. “Eighty-four per cent. of the cases occurred among those whose hands were contaminated by washing their own eating utensils.”
Among 17,236 employees of hotels, restaurants and department stores, who ate from machine washed dishes, there occurred 349 cases of influenza, while among 4,175 who ate from hand washed dishes there were 429 cases. The rate was but 20 per 1,000 in the former, while in the latter group it reached 103 per 1,000. Here again the chances of infection between the two groups were as one is to five.
These authors have records covering 252,186 individuals in scattered institutions in the United States. Among those eating from machine washed dishes the rate was 108 per 1,000 while those eating from hand washed dishes suffered at the rate of 324 per 1,000. The ratio was 1 to 3 between the two groups. Seventy-five per cent. of the cases occurred in that group which ate from dishes not disinfected with boiling water. They do not state the number of individuals in each of the two groups.
Lynch and Cumming claim that in the act of coughing only a few organisms are expelled from the mouth, rarely over 1,500, and conclude that transmission by direct contact through the air route but rarely, if ever, takes place. While about 1,500 organisms are expelled onto the floor by an act of coughing, a sterile glove wiped across the lips may pick up nearly 2,000,000 organisms. Such organisms may be readily transferred to inanimate objects which are handled by many people.
Hemolytic streptococci and pneumococci may be isolated with great regularity from the hands of carriers or patients, from table ware, inanimate objects touched by these patients, and from floor dust. Diphtheria and tubercle bacilli have been isolated from the hands and eating utensils of patients. The average count of a large number of restaurant dishwater specimens was 4,000,000 bacteria per c.c. The temperature of this water averaged 43° C. and the dishes were practically never scalded. The water was often so highly polluted, “that the dishes are more highly contaminated after they are washed than before washing begins. The spoon or fork is often freer from organisms just after being used by the restaurant patron than when taken from the restaurant’s polluted dish water.”
Major John S. Billings, epidemiologist at Camp Custer, reported that one of the larger organizations did not properly observe the regulation requiring that all mess kits and table equipment be properly sterilized. The disease appeared early and spread unusually rapidly in this particular organization.
In summarizing the subject of transmission through utensils, we may say that the evidence is suggestive but inconclusive. It is possible, even probable, that this is one mode of transmission. That it is the most important has not been proved. Lynch and Cumming do not take into consideration that the regiments with more sanitary methods of cleansing the dishes are apt to be those regiments with more sanitary habits throughout their daily routine. Those restaurants using mechanical dish washers are usually the cleaner restaurants.
Pontano in Italy is quoted by the Office International d’Hygiène Publique as having observed in his epidemiological study that there was a constant connection between the living conditions and the severity of the complications. Notable differences were observed in neighboring houses according to the hygienic conditions of the various households.
Healthy carriers and convalescents.—Leichtenstern, who apparently accepted the Pfeiffer bacillus as the cause of influenza, did not believe that the disease could be transmitted by healthy carriers. He based this assumption on the statement, made by Pfeiffer, that the influenza bacillus was only found in acute influenza cases. In the past few years it has been abundantly shown, however, that the influenza bacillus can and does exist on the mucous membranes of healthy individuals.
The outbreak in an orphan asylum in New Haven has been previously described. There the probable source of the sharp outbreak of December 27th seemed to be the sister who, on convalescence, resumed her duties in the kitchen. There she inspected and handled the milk served to the children. This suggests the possibility of infection being propagated by convalescents and by food.
At present we do not know whether or not a patient remains infectious after the acute symptoms have subsided; we are ignorant as to whether a convalescent patient can transmit the disease; and we are not certain whether the organism found in healthy carriers is virulent or not. The information at hand strongly indicates that apparently healthy individuals may transmit the infection, but the wide distribution of the disease, with multiple possible sources of infection for each individual, and the relative insusceptibility of experimentally exposed individuals has made it impossible so far to answer these questions satisfactorily.