PubMed · 15577933
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2004. Man versus microbe.. https://doi.org/10.1038/nm1149
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We reviewed the epidemiological and microbiological characteristics of 89 reported outbreaks of waterborne infectious intestinal disease affecting 4321 people in England and Wales over the period 1992-2003. Public water supplies were implicated in 24 outbreaks (27%), private water supplies in 25 (28%), swimming pools in 35 (39%) and other sources in five outbreaks (6%). Cryptosporidium was implicated in 69% of outbreaks, Campylobacter sp. in 14%, Giardia in 2%, E. coli O157 in 3% and Astrovirus in 1%. From 2000, there was a consistent decline in the number of outbreaks of waterborne disease associated with public water supplies. The incidence rate of outbreaks in recipients of private water supplies may be as high as 35 times the rate in those receiving public water supplies (1830 vs. 53 per million population). Private water suppliers need to be aware of the importance of adequate treatment and the prevention of faecal contamination of storage water. Swimming-pool operators need to ensure chlorination and in particular adequate filtration measures are in place.
An epidemic model with a generalized non-linear incidence is extended to incorporate the effect of an infection-dependent removal strategy, which is defined as a function of the number of infected individuals. It is assumed that the removal rate decreases from a maximum capacity for removing infected individuals as their number increases. The existence and stability of the associated equilibria are analysed, and the basic reproductive number (R0) is formulated. It is shown that R0 is independent of the functional form of the incidence, but depends on the removal rate. Normal forms are derived to show the different types of bifurcation the model undergoes, including transcritical, generalized Hopf (Bautin), saddle-node and Bogdanov-Takens. A degenerate Hopf bifurcation at the Bautin point, where the first Lyapunov coefficient vanishes, is discussed. Sotomayor's theorem is applied to establish a saddle-node bifurcation at the turning point of backward bifurcation. The Bogdanov-Takens normal form is derived, from which the local bifurcation curve for a family of homoclinic orbits is formulated. Bifurcation diagrams and numerical simulations, using parameter values estimated for some infectious diseases, are also presented to provide more intuition to the theoretical findings. The results show that sufficiently increasing the removal rate can reduce R0 below a subthreshold domain, which leads to disease eradication.
PURPOSE: The purpose of the study was (1) to identify the requirements for syndromic, disease surveillance and epidemiology systems arising from events such as the SARS outbreak in March 2003, and the deliberate spread of Bacillus anthracis, or anthrax, in the US in 2001; and (2) to use these specifications as input to the construction of a system intended to meet these requirements. An important goal was to provide information about the diffusion of a communicable disease without being dependent on centralised storage of information about individual patients or revealing patient-identifiable information. METHODS: The method applied is rooted in the engineering paradigm involving phases of analysis, system specification, design, implementation, and testing. The requirements were established from earlier projects' conclusions and analysis of disease outbreaks. The requirements were validated by a literature study of syndromic and disease surveillance systems. The system was tested on simulated EHR databases generated from microbiology laboratory data. RESULTS: A requirements list that a syndromic and disease surveillance system should meet, and an open source system, "The Snow Agent system", has been developed. The Snow Agent system is a distributed system for monitoring the status of a population's health by distributing processes to, and extracting epidemiological data directly from, the electronic health records (EHR) system in a geographic area. CONCLUSIONS: Syndromic and disease surveillance tools should be able to operate at all levels in the health systems and across national borders. Such systems should avoid transferring patient identifiable data, support two-way communications and be able to define and incorporate new and unknown diseases and syndrome definitions that should be reported by the system. The initial tests of the Snow Agent system shows that it will easily scale to national level in Norway.