Chlorination of Water Part 17

Some of the earlier results of the effect of chlorination on typhoid morbidity and mortality rates were compiled by Jennings[6] and others have been published by Longley.[7] These data have been brought up to date in Table x.x.xI and other statistics added.

TABLE x.x.xI.--EFFECT OF CHLORINATION ON TYPHOID RATES

AVERAGE TYPHOID DEATH RATE PER 100,000 POPULATION

----------------+-------------+--------------+--------------+----------- City. | Commenced | BEFORE USING.| AFTER USING. | |Chlorination.+-------+------+-------+------+ Percentage | |Period.|Rate. |Period.|Rate. | Reduction.

----------------+-------------+-------+------+-------+------+----------- Baltimore |June 1911 |1900-10| 35.2 |1912-15| 22.2 | 36 Cleveland |Sept. 1911 |1900-10| 35.5 |1912-16| 8.2 | 77 Des Moines |Dec. 1910 |1905-10| 22.7 |1911-13| 13.4 | 41 Erie |Mar. 1911 |1906-10| 50.6 |1912-14| 15.0 | 70 Evanston, Ill. |Dec. 1911 |1908-11| 29.0 |1912-13| 14.5 | 50 Jersey City |Sept. 1908 |1900-17| 18.7 |1909-16| 8.4 | 55 Kansas City, Mo.|Jan. 1911 |1900-10| 42.5 |1911-16| 14.2 | 66 Omaha, Neb. |May 1910 |1900-09| 22.5 |1911-16| 10.6 | 53 Trenton |Dec. 1911 |1907-11| 46.0 |1911-14| 28.7 | 35 Montreal |Feb. 1910 |1906-10| 40.0 |1911-16| 25.0 | 37 Toronto |Apr. 1911 |1906-10| 31.2 |1912-16| 7.8 | 75 Ottawa |Sept. 1912 |1906-10| 34.0 |1913-17| 17.0 | 50 ----------------+-------------+-------+------+-------+------+-----------

The figures given in this table show the effect of chlorination only; no other form of purification was used during the periods given, except at Toronto where a portion of the supply has been subjected to filtration.

It will be seen that since chlorination was adopted the typhoid death rates have been reduced by approximately 50 per cent and that the averages for the period after treatment are almost invariably less than 20 per 100,000, a figure that a few years ago was regarded as satisfactory. The average death rate for the last available year is 11 per 100,000, a result that is even more satisfactory and exceeds the antic.i.p.ations of the most optimistic of sanitarians.

A portion of the reduction in the typhoid rates is no doubt due to improvements in general sanitary conditions but the reduction is much greater than can be accounted for in that manner alone and in many cases there was a sharp decline immediately following the commencement of chlorination.

In a few instances there is evidence that chlorination has reduced the typhoid rates of cities previously supplied with filtered water. Diagram X, drawn from data supplied by Dr. West, of the Torresdale Filtration Plant, shows the effect of disinfecting the filter effluents at Philadelphia.

[Ill.u.s.tration: DIAGRAM X

TYPHOID IN PHILADELPHIA]

During the years 1909-10-11, when practically the whole of the city supply was filtered, the average typhoid death rate was 18, but when the water was also chlorinated, in 1914-15-16, the rate was only 7, a reduction of 61 per cent.

The figures in Table x.x.xII show that the Torresdale filters, during 1915-16 were unable to adequately purify the water and that chlorination was necessary.

TABLE x.x.xII.--CHLORINATION OF FILTER EFFLUENTS

(TORRESDALE)

----+---------+---------+----------+---------------------------------- | | | | BACTERIA PER CUBIC CENTIMETER.

| Oxygen | | +-----------------+---------------- |Consumed.| Colour. |Turbidity.| Untreated. | Treated.

| | | +---------+-------+---------+------ | | | |Gelatine.| Agar. |Gelatine.| Agar.

----+---------+---------+----------+---------+-------+---------+------ 1915| 1.70 | 12 | 0.6 | 141 | 30 | 28 | 14 1916| 1.90 | 12 | Nil. | 88 | 23 | 38 | 11 ====+=========+=========+==========+=========+=======+=========+====== | _B. coli communis_ | | Per Cent Positive Tests. | +----------------------+-------------------------+ | Untreated. | Treated. | Added Chlorine +----------+-----------+------------+------------+ Parts Per |10 c.cms. | 1 c.cm. | 10 c.cms. | 1 c.cm. | Million.

----+----------+-----------+------------+------------+---------------- 1915| 66 | 24 | 5 | 0.3 | 0.18 1916| 49 | 16 | 7.4 | 1.9 | 0.15 ----+----------+-----------+------------+------------+----------------

In Diagram XI the typhoid death rates of Columbus, Ohio, and New Orleans are shown to exemplify conditions that have not been improved by chlorination. The endemic condition of typhoid in Columbus was brought to an abrupt conclusion by the installation and operation of the softening and filter plant in September, 1908, and no further reduction followed the introduction of chlorination in December, 1909.

In New Orleans the typhoid rate decreased on the inception of the new water works system in 1909 and again after the installation of the Carrollton filters in 1912. The product of the filtration plants has always been above suspicion but aftergrowths occasionally developed and the bacterial count then exceeded the United States Treasury standard.

To overcome this difficulty, hypochlorite was used in 1915, but, as was antic.i.p.ated, it had no effect on the typhoid rate. The high rate in New Orleans is largely due to outside cases received for hospital treatment and to other circ.u.mstances beyond the control of the water and sewerage department.

In all the examples previously cited, the evidence as to the effect of chlorination on typhoid mortality rates is circ.u.mstantial but, taken as a whole, it is fairly conclusive. In the examples to be considered next the evidence is more direct.

[Ill.u.s.tration: DIAGRAM XI

TYPHOID IN COLUMBUS AND NEW ORLEANS]

One of the most conclusive experiments as to the beneficial effect of chlorination is that reported by Young[8] of Chicago. The water supply of Chicago was obtained from Lake Michigan by means of intake pipes and pumped to various parts of the city. The distribution system was divided into four districts and, although there was a certain amount of mixing along the borders, the water supplied to each district was substantially separate. The rapid and progressive decline in the typhoid rate of Chicago (from 19 in 1900 to 10.8 in 1911) subsequent to the diversion of the city sewage from the lake, led to the a.s.sumption that water-borne typhoid had ceased to be of any moment. Early in 1912, however, permission was secured to chlorinate the supply of one district (No. 1) and the treatment was continued until December when the solutions commenced to freeze. Diagram XII shows the effect of the treatment on the autumnal increase in District No. 1 as compared with the other three districts. The autumnal increase was calculated from the excess of typhoid incidence for July to November inclusive, over that for February to June inclusive.

[Ill.u.s.tration: DIAGRAM XII

AUTUMNAL INCREASE IN TYPHOID, CHICAGO (Young)]

These results demonstrate in a most striking manner the beneficial effect of chlorination. The general conditions, with the exception of the raw water supply, were approximately the same in all four districts.

Diagram XIII shows that the raw water supply of District No. 1 was slightly worse than any of the others, 21.8 per cent of the samples from District No. 1 containing _B. coli_ in 1 c.cm. as compared with 21.0 per cent in the most polluted supply of the other districts.

[Ill.u.s.tration: DIAGRAM XIII

B. COLI IN CHICAGO RAW WATER (Young)]

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 subst.i.tuted. The dosage has been so regulated as to a.s.sure 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.

[Ill.u.s.tration: 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 x.x.xIII that the improvement in the typhoid rate is immeasurably greater than can be ascribed to that cause.

TABLE x.x.xIII.--DEATH RATES IN OTTAWA BEFORE AND AFTER CHLORINATION

--------------------------+-------------------+--------------------- | RATE PER 100,000 | PERCENTAGE Cause. +---------+---------+-----------+--------- | 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 Diarrh[oe]a and Enteritis | 139 | 128 | 7.9 | ...

under 2 years | | | | --------------------------+---------+---------+-----------+---------

[A] Rate per 1,000.

[B] 1906-10, epidemic years 1911-12 excluded.

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.

In 1916 a liquid chlorine plant was installed in Hull, but in 1917, owing to an accident, it was out of commission for a short period and at least 100 cases of fever developed during the following month. During the same period only two cases were reported in Ottawa and of these one was obviously contracted outside the city.

In view of the preceding facts it must be granted that the improvement in the typhoid rate of Ottawa can be definitely attributed to an improvement in the water supply caused by chlorination.

The efficacy of chlorination to prevent and check epidemics of water-borne typhoid has never been doubted. Innumerable instances could be cited in which the prompt treatment of large public supplies has promptly checked outbreaks that threatened to a.s.sume serious proportions and there is no doubt that the extremely low typhoid morbidity rate on the Western Front of the European battlefield is partially due to the extensive and rigorous chlorination measures that have been instigated.

Prophylactic vaccination and the prompt isolation of typhoid carriers have largely contributed to the wonderful results obtained but due credit must also be given to the systematic purification and treatment of water supplies. Similar results have been obtained at training camps in Canada and in other countries by effective treatment with either liquid chlorine or hypochlorite.

Since the inception of water chlorination in America in 1908, the merit of the method has been very generally recognized throughout the Continent but was regarded with scepticism in Europe, except as a temporary expedient, until the results obtained by the military forces compelled more general recognition. Before the war, chlorination of water supplies in England was only practised in a few isolated and relatively unimportant instances; in 1917, practically the whole supply of London was chlorinated and at Worcester a similar treatment has been recommended to enable the slow sand filters to be operated at higher rates without reducing the quality of the water supplied to the consumers.

_Use and Abuse of Chlorine._ Inasmuch as chlorination has no beneficial effect on water except the reduction of the bacterial content it should be used for this purpose only and under such conditions as permit the operations to be under full control at all times. The supplies that can be most efficiently and safely treated are those that are relatively constant in chemical composition and bacterial pollution. Changes in volume can be dealt with by automatic apparatus but sudden changes in organic and bacterial content require a change of dosage that cannot be made by any mechanical appliance. Long experience and accurate meteorological records may in some cases enable those in charge of chlorination plants to antic.i.p.ate changes in the conditions of the water supply, but it is always preferable to provide a positive method of preventing sudden changes by using chlorination merely as an adjunct to other processes of purification. Unpurified waters that are objectionable on account of their bacterial content only are very rare, as the cause that produces the bacterial pollution usually produces other conditions that are equally objectionable though not so dangerous to health. Sudden storms in summer, or sudden thaws in winter, usually cause large increments in turbidity accompanied by soil was.h.i.+ngs that often carry appreciable quant.i.ties of faecal matter into surface water supplies. Lake supplies often suffer in the same manner and sewage, which during normal conditions is carried safely away from water intakes, obtains access to the supply. If the dosage is maintained at a level sufficiently high to meet these abnormal conditions, complaints as to taste and odour would ensue, and in general, such a practice is impossible. Some supplies have been chlorinated successfully for years but the principle of using chlorination as the first and last line of defence cannot be recommended. Success can only be obtained by eternal vigilance and the responsibility for results is more than water works officials should be called upon to a.s.sume.