Community Health Notes

NOTES NOTES COMMUNITY HEALTH DYNAMICS OF OUTBREAKS ▪ Outbreak: sudden increase in disease occurrence in a specific time, place, population (e.g. outbreaks of foodbornerelated norovirus acute gastroenteritis) ▪ Infective outbreaks depend on causative pathogen characteristics (such as mode of transmission) MODES OF INFECTIOUS DISEASE TRANSMISSION osms.it/transmission TRANSMISSION ▪ The passing of a pathogen-causing communicable disease from an infected host to another individual/group MODES OF TRANSMISSION ▪ Depends on responsible organism’s characteristics Direct ▪ Interpersonal contact → infected individuals spread disease ▫ One-to-one (e.g. venereal infection with sexual intercourse) ▫ One-to-multiple (e.g. influenza with a violent sneeze in a crowded environment) Indirect ▪ Common vehicle (e.g. contaminated air, water/food supply, needle-sharing) ▪ Vectors (e.g. mosquito/tick) OUTBREAK INVESTIGATIONS osms.it/outbreak-investigations CHARACTERISTICS OF AN OUTBREAK ▪ Explosive: in epidemic curve, there is a fast, abrupt rise in number of cases, followed by fast, abrupt fall ▪ Indirect transmission: infection limited to individuals who share common exposure 52 OSMOSIS.ORG ▪ Direct transmission: often impossible to associate new cases to primary case (first symptomatic case occurring in defined setting)

Chapter 7 Biostatistics & Epidemiology: Community Health STEPS TO INVESTIGATE AN OUTBREAK Validate outbreak’s existence in a population ▪ Define number of cases (numerator) ▪ Define the extent of the population susceptible to disease (denominator) ▪ Determine whether number of observed cases is more than expected number of cases ▪ Calculate the attack rate: proportion of an initially disease-free population that develops disease ▫ Proportion is used because the individuals in the numerator (those who have the disease) are included in the denominator (the total population) Investigate cases by looking for interactions of time, person, place ▪ Are there interactions between variables? Develop hypotheses ▪ Consider existing knowledge about the disease, findings from current investigation Test hypotheses ▪ Analyze data (e.g. case-control study, laboratory tests such as chemical/ immunological fingerprinting) Recommend measures for disease control, prevention ▪ E.g. remove infection source, establish environmental controls (interrupt disease transmission), improve sanitation, immunize susceptible individuals DISEASE SURVEILLANCE osms.it/disease-surveillance ▪ Essential public health tool, aimed at predicting, observing, minimizing outbreaks ▪ Based on systematic collection, analysis, interpretation of epidemiologic data ▪ Monitored parameters examples ▫ Changes in disease incidence/mortality ▫ Changes in quantity of risk factors for a disease in environment ▫ Completeness of vaccination coverage ▫ Prevalence of drug-resistant organisms MODALITIES OF SURVEILLANCE Passive ▪ Using existing data on reportable diseases such as anthrax, cholera, gonorrhea ▪ Pros ▫ Comparatively inexpensive, easy to develop ▫ Areas that require urgent intervention are quickly identified by international comparisons ▪ Cons ▫ Surveillance is not the primary responsibility of case-reporting individuals ▫ Local outbreaks may be missed Active ▪ Implementing surveillance program (e.g. field visits to clinics, hospitals, communities) ▪ Pros ▫ Reporting more accurate; individuals recruited specifically for surveillance program ▫ Local outbreaks are more likely to be identified ▪ Cons ▫ More expensive to develop, maintain DIFFICULTIES ▪ Obtaining reliable data in low-income countries → underreporting risk ▫ Areas may be difficult to reach ▫ Communication with central authorities can be challenging ▫ Resources such as diagnostic laboratories not always available OSMOSIS.ORG 53

VACCINATION & HERD IMMUNITY osms.it/vaccination-herd-immunity HERD IMMUNITY BASICS ▪ Herd immunity: phenomenon in which entire population is indirectly protected against disease when critical percentage of members are immune ▫ Immunity can be innate/acquired through vaccination/by naturally recovering from infection ▫ The higher the proportion of immune people in a population, the less likely the encounter between a susceptible person and an infected one → chain of infection is disrupted Conditions ▪ Host is a single species ▪ Transmission of the organism must be spread by direct contact ▪ No reservoir outside the human host ▪ Infections must induce solid immunity 54 OSMOSIS.ORG HERD IMMUNITY & COMMUNITY HEALTH ▪ The critical percentage of immune individuals needed to achieve herd immunity varies according to disease contagiousness (e.g. 94% in measles [highly communicable] → increased number of individuals need to be immune) ▪ Because of herd immunity, vaccination programs do not necessitate yield 100% immunization rates, yet can achieve highly effective protection by immunizing critical percentage of a population ▪ Herd immunity is important for public health because individuals who cannot develop immunity or cannot be vaccinated depend on herd immunity (e.g. newborn infants, individuals with immunodeficiency due to HIV/AIDS, cancer, cancer treatments)