introduction to Epi-Public Health & communicable disease_EUC_2023-2024_REVISION.pptx

Epidemiology/Public Health & Communicable Disease MED320 Dr Stavros Panagiotou in the 1830`s half of Manchester children died before their fifth birthday in Liverpool a laborer had a life expectancy of 15 years beginnings of public health control John Snow and the pump he is reputed to have loc...

Epidemiology/Public Health & Communicable Disease MED320 Dr Stavros Panagiotou in the 1830`s half of Manchester children died before their fifth birthday in Liverpool a laborer had a life expectancy of 15 years beginnings of public health control John Snow and the pump he is reputed to have locked up to prevent the spread of the public health movement resulted in Chadwick`s Public Health Act of 1848 focusing upon: • housing • sanitation • clean water The Domains of Public Health the epidemiological triad host agent environment main determinants influencing disease transmission: • agent – the organism that causes the infection • host – the potentially susceptible individual • environment – external factors that affect potential disease transmission the basic reproductive number: the number of new cases that occur in a totally susceptible population ….more commonly - the effective or net reproductive number: the number of new cases that occur in a population where there may be both susceptible and immune persons present immune suscepti ble infecte d reproductive number (R) in a totally susceptible population and in a population with 50% immunity R0 = basic reproductive number, R = net the net reproductive number is the basic reproductive number multiplied by the proportion of susceptible individuals for an infection to stop transmitting the effective reproductive number has to fall below one i.e. R <1 infections tend to die out when the reproductive number is less than average of 1 – however, this assumes a homogenous mixing pattern where all instances of contact in a population are equally likely and each individual has an equal chance of being infected in the real world, mixing patterns are not homogenous and transmission can therefore occur in groups where R >1, even though in the overall population the average for R may be <1 e.g. measles – ‘herd immunity’ * to measles is high in Wales due to good uptake of MMR vaccine – yet in Swansea in 2013 measles transmitted because there was a low uptake of MMR vaccine in that local area routes of transmission of infection: • direct  skin contact or touch (e.g. warts)  sexual intercourse (e.g. syphilis)  droplets (e.g. influenza)  faecal – oral (e.g. poliovirus)  transplacental (e.g. rubella, HIV) • indirect  fomites (e.g. bedding, toys, etc.,)  food or water (e.g. cholera, salmonella)  vectors (e.g. yellow fever)  blood borne (e.g. hepatitis B virus) the latent period: the time between infection and becoming infectious the incubation period: the time between infection and becoming symptomatic the infectious period: the time during which an infectious agent may be transferred from an infected person to another person if the latent period is less than the incubation period it becomes more difficult to control the infection as the infection can have spread before the index case shows symptoms – a good example is influenza where you become infectious before you develop symptoms the actual length of each of these periods will vary with the infectious organism and the infective dose consequences of infection infectious agent eliminated without the host developing symptoms or becoming infectious infectious agent colonises the host (remains within the host without causing disease) infection host develops asymptomatic infection and can be infectious host develops symptomatic infection and can be infectious occurrence of infection within a population sporadic: occasional cases occurring at irregular intervals endemic: persistent level of occurrence at low to moderate levels epidemic: occurrence in excess of the expected level of disease during a given time period pandemic: epidemic occurring in several countries the spread of infection from an infected individual to a susceptible individual is described in terms of the chain of infection control of infection necessitates breaking the chain host factors: o o o immunisation prophylaxis improving general health environmental factors - prevent or reduce contact between host and the infectious agent o barriers (condoms, PPE, etc.) o reduce amount of infectious agent reaching the host (hand washing, reduce overcrowding, sewage disposal, etc.,) agent factors - reduce amount of agent released o treat cases to reduce the infectious period o isolate cases o eliminate or reduce environmental reservoirs outbreak: o two or more people who experience a similar illness or confirmed infection, and are linked by a common factor or o when the observed number of cases unaccountably exceeds the expected number for a given time and place plotting an epidemic curve – a frequency distribution of date of onset – can help identify an incubation period which, when combined with analysis of the clinical features of the infection, can help identify the potential cause and source of the spread of infection There are 3 basic types of epidemic curve:- surveillance consequences of poor versus good surveillance: data collection: data is handled in accordance with the UK Data Protection Act 1998 and the Caldicott Guidelines (1997). •personal identifiers are held for the minimum time period consistent with their public health purpose (2 and 5 year rule) •access to databases are restricted to named individuals with a need to Know •postcode data is held in a way that individual patients cannot be traced but linkage to Geographical Information Systems, census and other datasets is retained •patient identifying data are not transmitted to others outside the HPA without the permission of the laboratory reporting to them