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Journal ArticleDOI

Intervention studies and the definition of dominant transmission routes

01 Sep 1984-American Journal of Epidemiology (Oxford University Press)-Vol. 120, Iss: 3, pp 449-455
TL;DR: The implications for the analysis of real-world data are analyzed by examining data on the importance of water and other transmission routes for cholera in Bangladesh by using a quantitative model to generate synthetic data.
Abstract: A common approach to assessing the relative importance of different transmission routes is to eliminate transmission through one route and assume that the ratio "number of cases eliminated:number of residual cases" measures the relative importance of the eliminated route vis-a-vis the residual transmission route. A quantitative model is used to generate synthetic data similar to those analyzed by epidemiologists. These data are analyzed using this conventional procedure and the inferences drawn from the synthetic data compared with the causal relationships structured into the model. The implications for the analysis of real-world data are analyzed by examining data on the importance of water and other transmission routes for cholera in Bangladesh.

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Posted ContentDOI
15 Mar 2021-medRxiv
TL;DR: The authors conducted a controlled before-and-after trial to evaluate the impact of an onsite urban sanitation intervention on the prevalence of enteric infection, soil transmitted helminth re-infection, and diarrhea among children in Maputo, Mozambique.
Abstract: We conducted a controlled before-and-after trial to evaluate the impact of an onsite urban sanitation intervention on the prevalence of enteric infection, soil transmitted helminth re-infection, and diarrhea among children in Maputo, Mozambique. A non-governmental organization replaced existing poor-quality latrines with pour-flush toilets with septic tanks serving household clusters. We enrolled children aged 1-48 months at baseline and measured outcomes before and 12 and 24 months after the intervention, with concurrent measurement among children in a comparable control arm. Despite nearly exclusive use, we found no evidence that intervention affected the prevalence of any measured outcome after 12 or 24 months of exposure. Among children born into study sites after intervention, we observed a reduced prevalence of Trichuris and Shigella infection relative to the same age group at baseline (

6 citations

Dissertation
17 Jul 2013
TL;DR: This thesis shows that transmission of influenza via surfaces may be less important than current infection control policies and public guidance documents imply.
Abstract: Limited understanding of influenza transmission has been a frequent obstacle during the development of pandemic influenza infection prevention and mitigation strategies. The science is hotly debated, especially the relative importance of transmission via large droplets or aerosols. Clarification of the relative importance of different modes of transmission is critical for the refinement of evidence-based infection control advice and has been called for by the European Center for Disease Control (ECDC), the World Health Organization (WHO), and the US Institute of Medicine. The primary aims of this thesis were to investigate influenza transmission; i) by obtaining data concerning viral shedding and the presence of influenza virus in the near environment of infected individuals and ii) through the exploration of a human challenge model to study transmission. Two major clinical studies have been performed; • Shedding and environmental deposition of novel A (H1N1) pandemic influenza virus. The primary aims of the study were to correlate the amount of virus detected in a subject’s nose with that recovered from his/her immediate environment (on surfaces and in the air) and with symptom duration and severity. Adults and children, both in hospital and from the community, who had symptoms of influenza infection were enrolled. Information about symptoms was collected and samples were taken including nose swabs, swabs from surfaces and air samples. Forty two subjects infected with influenza A(H1N1)pdm09 were recruited and followed up. The mean duration of nasal viral shedding was 6.2 days (by PCR) and 4.6 days (by culture). Over 25% of cases remained potentially infectious for at least 5 days. Symptom scores and viral shedding were poorly correlated. From surface swabs collected in the vicinity of 40 subjects, 15 (38%) subject locations were contaminated with virus. Overall 36 of 662 (5.4%) surface swabs taken were positive for influenza, two (0.3%) yielded viable virus. Subjects yielding positive surface samples had significantly higher nasal viral loads on illness Day 3 and more prominent respiratory symptom scores. Room air was sampled in the vicinity of 12 subjects and PCR positive samples were obtained from five (42%). Particles small enough to reach the distal lung (≤4µm) were found to contain virus. • Use of a human influenza challenge model to assess person-to-person transmission: Proof-of-concept study. The primary aim of this study was to establish that an experimentally induced influenza infection is transmissible. Healthy subjects deemed sero-susceptible to influenza A/H3N2/Wisconsin/67/2005 were intranasally inoculated (Donors) and when symptoms began, further sero-susceptible subjects (Recipients) were exposed to Donors during an ‘Exposure Event’. Subjects were in close contact, e.g. playing games and eating meals together, for a total of 28 hours during a 2 day period. Samples were collected to confirm infection status. Among 24 healthy adult subjects, nine were randomised to the ‘Donor’ group and 15 to the ‘Recipient’ group. Following inoculation 5 out of 9 Donors (55%) developed illness and 7 out of 9 (78%) were proven to be infected. After exposure, 5 out of 15 Recipients developed symptoms and 3 out of 15 were proven to be infected. Three others were found to be non sero-susceptible prior to exposure. The overall attack rate in Recipients was 20% but was 25% after adjustment for pre-exposure immunity. The contact, droplet and aerosol routes of influenza transmission are all likely to have a role. This thesis shows that transmission of influenza via surfaces may be less important than current infection control policies and public guidance documents imply. Air sampling results add to the accumulating evidence that supports the potential for aerosol transmission of influenza. The human challenge model could be used to investigate routes of influenza transmission further and a study funded by the Centers for Disease Control (CDC) is planned.

6 citations


Cites background from "Intervention studies and the defini..."

  • ...For example if contact transmission is blocked by hand hygiene, transmission could still occur via droplets and aerosols making the interpretation of any risk reduction complex (Briscoe 1984)....

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Posted Content
TL;DR: The data suggest that wealthier households are no less decisions and problems outside the realm of the vulnerable to illness and the water sources that supply the household, including the performance of the waterwealthy (the water company and private wells) are company.
Abstract: Summary findings Alberini, Eskeland, Krupnick, and McGranahan develop disrupted more often, interfering with their defensiveand estimate a model of household defensive behavior behavior.and illness. Using cross-section data from a household There is also evidence, although weak, to supportsurvey in Jakarta, they observe defensive behavior findings by van der Slice and Briscoe (1993): that(washing hands after using the toilet) consistent with pathogens originating within a household are lessexpectations: Defensive effort intensifies with exposure harmful to household members than are pathogensto contamination, and with income and education. originating from other households.Variables associated with the cost of defensive Given the opportunity and knowledge, individuals trybehavior - such as interruptions in the water supply- to modify the effect of contamination on the incidence ofreduce defensive behavior. diarrhea. But diarrhea's incidence is also affected byThe data suggest that wealthier households are no less decisions and problems outside the realm of thevulnerable to illness. The water sources that supply the household, including the performance of the waterwealthy (the water company and private wells) are company.This paper

4 citations

Journal ArticleDOI
TL;DR: In this article, the authors evaluated the water quality in drinking water or raw water supplies in the Colombian Caribbean region using the risk index for water quality (IRCA) and water quality index (IAP) proposed by CETESB, Brazil.
Abstract: The water quality in drinking water or raw water supplies in the Colombian Caribbean region was evaluated using the risk index for water quality (IRCA) and the water quality index (IAP) proposed by CETESB, Brazil. The following towns were selected: Mahates, supplied with surface water from the Canal del Dique, San Joaquin, Malagana and San Basilio de Palenque, which use groundwater, and Mandinga, supplied by an artisanal dam. Physical and chemical parameters, heavy metals, microbiological parameters (total coliforms and Escherichia coli) and pesticides (organochlorine and organophosphorus compounds) used in the region for agriculture and livestock were determined. Groundwater showed a high hardness and surface water a high turbidity. Critical concentrations of pesticides were not detected, but microbiological contamination was found in water supplies and aqueducts, as well as Fe, Cr and Ni levels in water supplies, and Pb and Ni in aqueducts, higher than those allowed by both quality indices. The water supplies of the towns presented unsafe IRCA and IAP in the majority cases. This investigation studied the contamination in water supplies and aqueducts in the Colombian Caribbean region to provide environmental authorities with the necessary information to establish strategies and regulations to reduce the risks of water contamination.

4 citations


Additional excerpts

  • ...1991; Briscoe 1984)....

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References
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Book
06 Mar 2012
TL;DR: It would occupy a long time to give an account of the progress of cholera over different parts of the world, with the devastation it has caused in some places, whilst it has passed lightly over others, or left them untouched; and unless this account could be accompanied with a description of the physical condition of the places, and the habits of the people, which I am unable to give, it would be of little use.
Abstract: It would occupy a long time to give an account of the progress of cholera over different parts of the world, with the devastation it has caused in some places, whilst it has passed lightly over others, or left them untouched; and unless this account could be accompanied with a description of the physical condition of the places, and the habits of the people, which I am unable to give, it would be of little use. There are certain circumstances, however, connected with the progress of cholera, which may be stated in a general way. It travels along the great tracks of human intercourse, never going faster than people travel, and generally much more slowly. In extending to a fresh island or continent, it always appears first at a sea-port. It never attacks the crews of ships going from a country free from cholera to one where the disease is prevailing, till they have entered a port, or had intercourse with the shore. Its exact progress from town to town cannot always be traced; but it has never appeared except where there has been ample opportunity for it to be conveyed by human intercourse. There are also innumerable instances which prove the communication of cholera, by individual cases of the disease, in the most convincing manner. Instances such as the following seem free from every source of fallacy. I called lately to inquire respecting the death of Mrs. Gore, the wife of a labourer, from cholera, at New Leigham Road, Streatham. I found that a son of deceased had been living and working at Chelsea. He came home ill with a bowel complaint, of which he died in a day or two. His death took place on August 18th. His mother, who attended on him, was taken ill on the next day, and died the day following (August 20th). There were no other deaths from cholera registered in any of the metropolitan districts, down to the 26th August, within two or three miles of the above place; the nearest being

1,203 citations

Journal ArticleDOI
TL;DR: The spectrum of illness and the immunologic response produced by cholera in volunteers were studied and Titers of vibriocidal antibody rose after diarrhea, peaked the second week after challenge, and rapidly fell during the next four weeks.
Abstract: The spectrum of illness and the immunologic response produced by cholera in volunteers were studied. The strains of Vibrio cholerae used were classical Inaba 569B and classical Ogawa 395. An oral dose of 108 organisms in buffered saline was required to induce the diarrhea of cholera. When given with live organisms, NaHCO3 lowered the infecting dose from 108 to 104 organisms. Clinical manifestations of infection varied from culturally positive formed stools to "rice water" diarrhea. Severe diarrhea did not have an explosive onset but rather progressively increased in volume during a 24-hr period. In 45% of cases the stool was positive for V. cholerae before the onset of diarrhea. Titers of vibriocidal antibody rose after diarrhea, peaked the second week after challenge, and rapidly fell during the next four weeks.

317 citations

Journal Article
TL;DR: A preliminary attempt to validate this model using published data on sanitation level, life expectancy, and adult literacy rates, for 65 developing countries appears to provide preliminary support for the threshold saturation theory but further empirical validation is required before a quantitative predictive model can be developed.
Abstract: A general theory on the relationship between water supply and sanitation investments and health, the threshold-saturation theory, is proposed. The theory takes into consideration three variables: health status, socioeconomic status, and sanitation level, and attempts to encompass, for the first time in one general theoretical framework, numerous conflicting empirical findings. The two-tiered S-shaped logistic form of the relationship that is proposed assumes that at the lower end of the socioeconomic spectrum there is a threshold below which investments in community water supplies and/or excreta disposal facilities alone result in little detectable improvement in health status. Similarly, at the higher end of the socioeconomic scale, it is suggested that a point of saturation is reached beyond which further significant health benefits cannot be obtained by investments in conventional community sanitation facilities. A preliminary attempt to validate this model using published data on sanitation level (defined as access to water supply), life expectancy, and adult literacy rates, for 65 developing countries, appears to provide preliminary support for the threshold saturation theory but further empirical validation is required before a quantitative predictive model can be developed.

83 citations

Journal Article
TL;DR: Results show that cholera transmission was via contaminated surface water, particularly water taken into households for cooking or drinking, and the frequency of exposure appeared to be a major determinant of the infection rate.
Abstract: The apparent failure of handpump tubewells to reduce the incidence of cholera among users in the flooded rural area of Bangladesh has stimulated interest in defining precisely the means of Vibrio cholerae transmission during localized outbreaks. Cholera-infected neighbourhoods were placed under intensive microbiological surveillance to pinpoint contaminated sources and subsequent infections. The results show that cholera transmission was via contaminated surface water, particularly water taken into households for cooking or drinking. Infections resulted from a daily dose not exceeding 105 organisms and the frequency of exposure appeared to be a major determinant of the infection rate. The importance of these data in environmental interventions and particularly in the provision of tubewells is discussed.

70 citations


"Intervention studies and the defini..." refers background in this paper

  • ...This example is of particular interest because, through a remarkable recent microbiological-cum-epidemiologic study in Matlab (11), direct microbiologic data are available on the frequency with which V....

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  • ...However, the microbiologic data (11) and our model indicate that improving the quality of drinking water did effect a major reduction in exposure to V....

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Journal ArticleDOI
TL;DR: Luecke and McGinn as mentioned in this paper showed that many "no significant effect" findings may be artifacts of statistical techniques used to analyze cross-sectional survey data, and compared the statistics thus yielded with their knowledge of the causal relationships programmed into the data.
Abstract: Many studies have purported to demonstrate that schooling has little independent impact on achievement and that administrators can do little to boost students' test scores. Daniel F. Luecke and Noel F. McGinn question such results and use variations of a computer simulation model to generate data sets similar to those collected by educational researchers. They subject the data generated to several kinds of aggregation procedures and regression analysis, and compare the statistics thus yielded with their knowledge of the causal relationships programmed into the data. They conclude that many "no significant effect" findings may be artifacts of statistical techniques used to analyze cross-sectional survey data.

30 citations