As regards diphtheria, the chief causes of the spread of this disease are mistaken diagnosis, imperfect isolation, incomplete disinfection, and, paradoxical though it may seem, a lack of susceptibility to the disease in a large number of children.
Many physicians are still under the grave error that diphtheria can always be recognised without the aid of the microscope, and that membranous croup commonly kills. All scientific writers upon diphtheria agree that it is caused by the Klebs-Loeffler bacillus. They also hold that there is a disease called membranous croup, as distinct from diphtheria as typhoid is, but that membranous croup is a comparatively harmless and non-contagious disease. Two per centum is a liberal mortality in membranous croup, yet a certain class of physicians are constantly reporting deaths from this disease. In a series of 286 cases (not deaths) diagnosed as membranous croup by physicians of New York [{188}] City a few years ago, Park found the diphtheria bacillus in 229, or 80 per centum. I have never examined the throat of a child dead from so-called membranous croup in which I did not find the diphtheria bacillus. This is the experience of almost every bacteriologist who has had to do with diphtheria. Some men report deaths from diphtheria as thrush! These deaths might just as truthfully be attributed to the wearing of linen collars.
On the other hand, according to Baginsky of Berlin, Martin of Paris, Park of New York, and Morse of Boston, from 20 to 50 per centum of the cases admitted even to diphtheria hospitals have not diphtheria at all. Bacteriologists find that about 35 per centum of the cases reported by physicians to be diphtheria are really nothing but tonsilitis or pharyngitis, with now and then a case of membranous croup. Without a bacteriological diagnosis, therefore, 35 families in each 100 quarantined (where quarantine laws exist) are unjustly quarantined and subjected to the trouble and expense of useless disinfection. The suffering this can cause to a poor family, whose small business is often ruined by quarantine, is a matter for very serious consideration. Again, no matter what experience a physician may have had, he can not in many cases differentiate diphtheria in its early stages, or in children of good resisting power, from comparatively harmless throat affections. The extraordinary resisting power against diphtheria shown by some children and adults has been described by Wassermann (Zeitschrift f. Hyg., 19 B., 3 H.). He found one series of 17 children, from one and a half to eleven years of age, and 34 adults, in which 11 children and 28 adults were not only immune to diphtheria, but some of them had enough antitoxin in their blood to neutralise a tenfold fatal dose of diphtheria toxin. This explains many mysterious outbreaks of diphtheria: such immune persons are infected and they carry about the disease unconsciously because they are not ill themselves. I have seen a mother kiss a child dying of malignant diphtheria and the woman did not get even a sore throat, but I know of another case exactly like this in which the mother died from the infection.
There are bad cases of diphtheria which the experienced physician can diagnose as soon as he enters the patient's room without even looking at the throat, but the lighter cases that are dangerous are not easily recognised. I have seen two children of a family in Washington attacked with a slight throat soreness after one child had died of diphtheria in the house. The cases of these two children would never even suggest diphtheria if that first child had not had the disease. Both these patients died within ten days of syncope without the formation of any membrane, but the diphtheria bacillus was present microscopically. To the moment of death there was nothing in the symptoms of these two children to show diphtheria to the naked eye. From a personal experience with more than 800 cases of diphtheria in hospitals and as a medical inspector, I feel certain that light attacks of diphtheria can not be diagnosed without the aid of the microscope.
The immunity mentioned above explains the fact that the Klebs-Loeffler bacillus is sometimes found in healthy throats, and the person that has such a throat is really more dangerous than a patient that is ill with diphtheria, because we cannot guard ourselves against him. School-children at times have what appears to be mere sore throat but which is really diphtheria in the naturally immune.
All cases of sore throat in school-children should be examined bacteriologically, but unfortunately the bacteriological examination for diphtheria is a complicated process which requires an expert bacteriologist and a laboratory. The cost of a laboratory fitted for this diagnosis alone is not great, but it is not easy to persuade small city governments that they need such plants.
The only resource, then, is to treat every suspicious case of sore throat as if the disease were really diphtheria, until a diagnosis is established as near the truth as possible. Children that are afflicted with throat inflammations should be kept from school. The people should be taught the necessity of isolation and disinfection; they should be warned against patent disinfectants, and told to ask competent physicians to advise them in disinfection.
Diphtheria is not directly caused by unhygienic surroundings. A disregard for hygiene disposes a child for infection if the child is exposed to the bacillus. The specific germ must be introduced into the patient's mouth or nostrils. When a child is infected with diphtheria the breath is not a medium of contagion. The sputum, spat out or coughed out, is a means whereby the disease is spread. The bacillus is in the patient's mouth and nostrils; it gets upon his hands by contact, upon eating utensils, upon whatever touches the mouth of the sick person. The bacillus does not float in the air of even the sick-room, except in those cases where dried sputum is stirred up by sweeping or attrition of other kinds.