1905, following an outbreak of typhoid fever, the city of lincoln, england, instituted permanent water chlorination. the first permanent disinfection of drinking water in the us was made in 1908 to the jersey city, new jersey, water supply. credit for the decision to build the chlorination system has been given to john l. leal. the chlorination facility was designed by george w. fuller. outbreaks in traveling military groups led to the creation of the lyster bag in 1915; a bag with a faucet which can be hung from a tree or pole, filled with water, and comes with a chlorination tablet to drop into the water. the lyster bag was essential for the survival of american soldiers in the vietnam war. direct transmission and carriers mary mallon ("typhoid mary") in a hospital bed (foreground): she was forcibly quarantined as a carrier of typhoid fever in 1907 for three years and then again from 1915 until her death in 1938. there were several occurrences of milk delivery men spreading typhoid fever throughout the communities they served. although typhoid is not spread through milk itself, there were several examples of milk distributors in many locations watering their milk down with contaminated water, or cleaning the glass bottles the milk was placed in with contaminated water. boston had two such cases around the turn of the 20th century. in 1899 there were 24 cases of typhoid traced to a single milkman, whose wife had died of typhoid fever a week before the outbreak. in 1908, j.j. fallon, who was also a milkman, died of typhoid fever. following his death and confirmation of the typhoid fever diagnosis, the city conducted an investigation of typhoid symptoms and cases along his route and found evidence of a significant outbreak. a month after the outbreak was first reported, the boston globe published a short statement declaring the outbreak over, stating "t jamaica plain there is a slight increase, the total being 272 cases. throughout the city there is a total of 348 cases." there was at least one death reported during this outbreak: mrs. sophia s. engstrom, aged 46. typhoid continued to ravage the jamaica plain neighborhood in particular throughout 1908, and several more people were reported dead due to typhoid fever, although these cases were not explicitly linked to the outbreak. the jamaica plain neighborhood at that time was home to many working-class and poor immigrants, mostly from ireland. the most notorious carrier of typhoid fever, but by no means the most destructive, was mary mallon, known as typhoid mary. although other cases of human-to-human spread of typhoid were known at the time, the concept of an asymptomatic carrier, who was able to transmit disease, had only been hypothesized and not yet identified or proven. mary mallon became the first known example of an asymptomatic carrier of an infectious disease, making typhoid fever the first known disease being transmissible through asymptomatic hosts. the cases and deaths caused by mallon were mainly upper-class families in new york city. at the time of mallon's tenure as a personal cook for upper-class families, new york city reported 3,000 to 4,500 cases of typhoid fever annually. in the summer of 1906 two daughters of a wealthy family and maids working in their home became ill with typhoid fever. after investigating their home water sources and ruling out water contamination, the family hired civil engineer george soper to conduct an investigation of the possible source of typhoid fever in the home. soper described himself as an "epidemic fighter". his investigation ruled out many sources of food, and led him to question if the cook the family hired just prior to their household outbreak, mallon, was the source. since she had already left and begun employment elsewhere, he proceeded to track her down in order to obtain a stool sample. when he was able to finally meet mallon in person he described her by saying "mary had a good figure and might have been called athletic had she not been a little too heavy." in recounts of soper's pursuit of mallon, his only remorse appears to be that he was not given enough credit for his relentless pursuit and publication of her personal identifying information, stating that the media "rob me of whatever credit belongs to the discovery of the first typhoid fever carrier to be found in america." ultimately, 51 cases and 3 deaths were suspected to be caused by mallon. in 1924 the city of portland, oregon, experienced an outbreak of typhoid fever, consisting of 26 cases and 5 deaths, all deaths due to intestinal hemorrhage. all cases were concluded to be due to a single milk farm worker, who was shedding large amounts of the typhoid pathogen in his urine. misidentification of the disease, due to inaccurate widal test results, delayed identification of the carrier and proper treatment. ultimately, it took four samplings of different secretions from all of the dairy workers in order to successfully identify the carrier. upon discovery, the dairy worker was forcibly quarantined for seven weeks, and regular samples were taken, most of the time the stool samples yielding no typhoid and often the urine yielding the pathogen. the carrier was reported as being 72 years old and appearing in excellent health with no symptoms. pharmaceutical treatment decreased the amount of bacteria secreted, however, the infection was never fully cleared from the urine, and the carrier was released "under orders never again to engage in the handling of foods for human consumption." at the time of release, the authors noted "for more than fifty years he has earned his living chiefly by milking cows and knows little of other forms of labor, it must be expected that the closest surveillance will be necessary to make certain that he does not again engage in this occupation." overall, in the early 20th century the medical profession began to identify carriers of the disease, and evidence of transmission independent of water contamination. in a 1933 american medical association publication, physicians' treatment of asymptomatic carriers is best summarized by the opening line "carriers of typhoid bacilli are a menace". within the same publication, the first official estimate of typhoid carriers is given: 2 to 5% of all typhoid patients, and distinguished between temporary carriers and chronic carriers. the authors further estimate that there are four to five chronic female carriers to every one male carrier, although offered no data to explain this assertion of a gender difference in the rate of typhoid carriers. as far as treatment, the authors suggest: "when recognized, carriers must be instructed as to the disposal of excreta as well as to the importance of personal cleanliness. they should be forbidden to handle food or drink intended for others, and their movements and whereabouts must be reported to the public health officers". new typhoid carrier cases reported in l.a. county between 2006 and 2016 today, typhoid carriers exist all over the world, but the highest incidence of asymptomatic infection is likely to occur in south/southeast asian and sub-saharan countries. the los angeles county department of public health tracks typhoid carriers and reports the number of carriers identified within the county yearly; between 2006 and 2016 0-4 new cases of typhoid carriers were identified per year. cases of typhoid fever must be reported within one working day from identification. as of 2018, chronic typhoid carriers must sign a "carrier agreement" and are required to test for typhoid shedding twice yearly, ideally every 6 months. carriers may be released from their agreements upon fulfilling "release" requirements, based on completion of a personalized treatment plan designed with medical professionals. fecal or gallbladder carrier release requirements: 6 consecutive negative feces and urine specimens submitted at 1-month or greater intervals beginning at least 7 days after completion of therapy. urinary or kidney carrier release requirements: 6 consecutive negative urine specimens submitted at 1-month or greater intervals beginning at least 7 days after completion of therapy. as of 2016 the male:female ratio of carriers in los angeles county was 3:1. due to the nature of asymptomatic cases, many questions remain about how individuals are able to tolerate infection for long periods of time, how to identify such cases, and efficient options for treatment. researchers are currently working to understand asymptomatic infection with salmonella species by studying infections in laboratory animals, which will ultimately lead to improved prevention and treatment options for typhoid carriers. in 2002, john gunn described the ability of salmonella sp. to form biofilms on gallstones in mice, providing a model for studying carriage in the gallbladder. denise monack and stanley falkow described a mouse model of asymptomatic intestinal and systemic infection in 2004, and monack went on to demonstrate that a sub-population of superspreaders are responsible for the majority of transmission to new hosts, following the 80/20 rule of disease transmission, and that the intestinal microbiota likely plays a role in transmission. monack's mouse model allows long-term carriage of salmonella in mesenteric lymph nodes, spleen and liver. vaccine development almroth edward wright developed the first effective typhoid vaccine. british bacteriologist almroth edward wright first developed an effective typhoid vaccine at the army medical school in netley, hampshire. it was introduced in 1896 and used successfully by the british during the second boer war in south africa. at that time, typhoid often killed more soldiers at war than were lost due to enemy combat. wright further developed his vaccine at a newly opened research department at st mary's hospital medical school in london from 1902, where he established a method for measuring protective substances (opsonin) in human blood. wright's version of the typhoid vaccine was produced by growing the bacterium at body temperature in broth, then heating the bacteria to 60 °c to "heat inactivate" the pathogen, killing it, while keeping the surface antigens intact. the heat-killed bacteria was then injected into a patient. to show evidence of the vaccine's efficacy, wright then collected serum samples from patients several weeks post-vaccination, and tested their serum's ability to agglutinate live typhoid bacteria. a "positive" result was represented by clumping of bacteria, indicating that the body was producing anti-serum (now called antibodies) against the pathogen. citing the example of the second boer war, during which many soldiers died from easily preventable diseases, wright convinced the british army that 10 million vaccine doses should be produced for the troops being sent to the western front, thereby saving up to half a million lives during world war i. the british army was the only combatant at the outbreak of the war to have its troops fully immunized against the bacterium. for the first time, their casualties due to combat exceeded those from disease. in 1909, frederick f. russell, a u.s. army physician, adopted wright's typhoid vaccine for use with the army, and two years later, his vaccination program became the first in which an entire army was immunized. it eliminated typhoid as a significant cause of morbidity and mortality in the u.s. military. typhoid vaccination for members of the american military became mandatory in 1911. before the vaccine, the rate of typhoid fever in the military was 14,000 or greater per 100,000 soldiers. by world war i, the rate of typhoid in american soldiers was 37 per 100,000. during the second world war, the united states army authorized the use of a trivalent vaccine – containing heat-inactivated typhoid, paratyphi a and paratyphi b pathogens. in 1934, discovery of the vi capsular antigen by arthur felix and miss s. r. margaret pitt enabled development of the safer vi antigen vaccine – which is widely in use today. arthur felix and margaret pitt also isolated the strain ty2, which became the parent strain of ty21a, the strain used as a live-attenuated vaccine for typhoid fever today. antibiotics and resistance chloramphenicol was isolated from streptomyces by david gotlieb during the 1940s. in 1948 american army doctors tested its efficacy in treating typhoid patients in kuala lumpur, malaysia. individuals who received a full course of treatment cleared the infection, whereas patients given a lower dose had a relapse. asymptomatic carriers continued to shed bacilli despite chloramphenicol treatment - only ill patients were improved with chloramphenicol. resistance to chloramphenicol became frequent in southeast asia by the 1950s, and today chloramphenicol is only used as a last