The results obtained at Ottawa are also conclusive. Following two epidemics of typhoid fever in 1911 and 1912, caused by breaks in the intake pipe, hypochlorite treatment was commenced and has been in continuous operation until February, 1917, when chloramine treatment was substituted. The dosage has been so regulated as to assure a high degree of purity at all times in the water delivered to the mains and as evidence of this it might be mentioned that the average B. coli index (calculated by Phelps’ method) for the years 1916 and 1917 was only 0.27 per 100 c.cms. The typhoid rates for the five years preceding the epidemic years and for a similar subsequent period are given in [Diagram XIV].
DIAGRAM XIV
TYPHOID IN OTTAWA
The diagram shows that there has been a constant reduction in the city typhoid rate since the last severe epidemic with the exception of the year 1915. The high rate of that year was caused by a localised epidemic started by polluted well water and spread by flies from an unsewered area. This outbreak was the cause of about seven deaths registered during that year (population 100,000).
The objection might be raised that if the reduction of the typhoid rate were due to the water treatment, the decline should have been abrupt and not a gradual one. It is probable that there has been practically no water-borne typhoid in the city since chlorination was commenced but this fact is masked by cases from other sources. During 1911 and 1912 over 3,500 cases of typhoid were reported, of which an appreciable number would become carriers for various periods of time. As these carriers decreased the number of cases infected by them would also decrease and so account for a gradually declining death rate.
It might be further objected that the reduced typhoid rate is due to a general improvement in the sanitary conditions. If the death rate from causes other than typhoid can be regarded as a measure of the general sanitary conditions it is obvious from the data in [Table XXXIII] that the improvement in the typhoid rate is immeasurably greater than can be ascribed to that cause.
TABLE XXXIII.—DEATH RATES IN OTTAWA BEFORE AND
AFTER CHLORINATION
| Cause. | Rate Per 100,000 | Percentage | ||||
| 1908-12 | 1913-17 | Reduction | Increase | |||
| Total[A] | 14 | .90 | 14 | .78 | 1.2 | ... |
| Typhoid, total | 34 | [B] | 17 | 50.0 | ... | |
| Typhoid, city | 26 | [B] | 8 | 69.2 | ... | |
| Pneumonia | 100 | 107 | ... | 7.0 | ||
| Tuberculosis | 133 | 138 | ... | 3.7 | ||
| Diarrhœa and Enteritis under 2 years | 139 | 128 | 7.9 | ... | ||
| [A]Rate per 1,000. | ||||||
| [B] 1906-10, epidemic years 1911-12excluded. | ||||||
One further objection might be made: that the raw water was not infected during 1913-17 or infected to a smaller extent than during the previous period. Attempts to isolate B. typhosus from the raw water have invariably been futile but their presence in 1914 might be inferred from the fact that during the latter part of the summer of that year an epidemic of typhoid fever occurred at Aylmer, a village that discharges its sewage into the Ottawa River about six miles above the Ottawa intake. Hull, situated on the opposite bank of the river and having a population of 20,000, takes its water supply from the same channel that supplies Ottawa but at a point a few hundred feet further down stream. During November and December, 1914, some 200 cases of typhoid fever (incidence 1,000 per 100,000) occurred in Hull as compared with 28 in Ottawa. As the Ottawa intake is situated between the Hull intake and the outlet of the Aylmer sewer it is incredible that the Ottawa raw water was not also infected.