MCB2004 Microbiology for Health Services Exam #3 Study Guide 1 1. Know which type of nosocomial infection is most common Urinary tract infections (UTIs) are most common nosocomial infection (32%) • Probably because so many people have urinary catheters inserted during a hospital stay 2. Know what medical procedure most increases the likelihood of an infection Hemodialysis is the procedure that increases the likelihood of infection the most • Involves filtering patients blood supply – lots of opportunities for infection 3. Know the definitions of sporadic disease, endemic disease, epidemic disease, pandemic disease. Be able to recognize at least 1 example of each. Know the definition of herd immunity. Sporadic Disease: Disease that occurs occasionally in a population • Ex) Sporadic outbreaks of Ebola virus every few years in Central Africa Endemic Disease: Disease that is constantly present in a population at a low rate • Ex) Vibrio cholerae is an endemic cause of gastrointestinal disease in South Asia o South Asia has reservoirs (marine life) became endemic o Became an epidemic when introduced in Haiti Could become endemic to Haiti in the future Could disappear if it doesn’t find a reservoir Epidemic Disease: Disease acquired by many hosts in a given area in a short time • Ex) Poorly drained sewage from the UN peacekeepers camp led to an epidemic of Vibrio cholerae-caused gastrointestinal disease in Haiti Pandemic Disease: Worldwide epidemic • Ex) In 1918, a strain of influenza virus caused a worldwide pandemic • Ex) HIV is slow-moving pandemic Herd Immunity: Majority of the population has immunity to the disease either from having the infection or being immunized • If the infected person only encounters people who have been immunized, none of them should contract the disease or become carriers • If the infected person encounters people who haven’t been immunized, they can contract it and become carriers 4. Know the definition of ‘pathology’ and the definition of ‘etiology’ Pathology: The study of disease Etiology: The study of the cause of a disease • AIDS is a disease & HIV is the cause of it 5. Know the definition of ‘incidence’ of a disease and the definition of ‘prevalence’ of a diseaseMCB2004 Microbiology for Health Services Exam #3 Study Guide 2 The incidence of a disease is the fraction of a population that contracts a disease during a specific time • Specific time frame when the disease was contracted • How many people contracted influenza in this past week? The prevalence of a disease is the fraction of the population having a specific disease at a given time • Sum total of all the people who have the disease at a time • Doesn't matter when they contracted it • How many people have influenza at this moment? Ability to determine incidence & prevalence is only as good as the diagnostics available 6. Know the definition of ‘morbidity’ and the definition of ‘mortality’ Morbidity: Incidence of a specific notifiable (physicians required to report) disease Mortality: Deaths caused by notifiable diseases 7. Know the definition of ‘sign’ and the definition of ‘symptom’ Sign: A change in the body that can be measured or observed as a result of disease • Ex) Heart rate Symptom: A change in body function that is felt by a patient as a result of disease • Have to rely on patient to report • Unconscious patients cannot report symptoms • Ex) Pain 8. Know the definitions of ‘parasitism’, ‘commensalism’, and ‘mutualism’ Symbiosis Parasitism: One organism benefits at the expense of the other Commensalism: One organism benefits and the other is unaffected • Difficult to classify o Might be subtle harm we don’t know about Mutualism: Both organisms benefit 9. Know Koch’s postulates Koch’s Postulates 1. The same pathogen must be present in every case of the disease 2. The pathogen must be isolated from the diseased host and grown in pure culture 3. The pathogen from the pure culture must cause the disease when it is inoculated into a healthy, susceptible lab animal 4. The pathogen must be isolated from the inoculated animal and shown to be the same as the original pathogenMCB2004 Microbiology for Health Services Exam #3 Study Guide 3 10. From the history of epidemiology, know what Nightingale studied, and what was her major novel contribution to epidemiological methods. Florence Nightingale – nurse among British troops in Crimean war • Tracked infection rates by month over time • Showed that one factor influencing infection rates is temperature o Infection rates increased in warmer months • Major contribution = improving sanitation methods o Showed that improved sanitation decreased the incidence of epidemic typhus 11. Know what Semmelweis studied and what was his major novel contribution to epidemiological methods Ignaz Semmelweis • Showed that handwashing by doctors decreased the incidence of spreading puerperal fever – infections after giving birth • Controlled experiment o Tracked when he washed his hands and when he didn't, when disease occurred and when it didn't 12. Know the definition of ID50 and LD50 ID50: Infectious dose required for 50% of the test population to be made sick • Ex) Norovirus has very low ID50 – very easy to become infected LD50: Lethal dose of a toxin for 50% of the test population • Toxin/drug • Dose that is enough to kill • Dependent on portal of entry o Ex) Anthrax spores For skin infection, very low LD50 (easily lethal) For inhalation, very high LD50 (not very lethal, good thing) ID50 & LD50 always defined in terms of a population The smaller the difference between ID50 & LD50, the more toxic the substance 13. Know what a microbial adhesin does Adhesins (ligands) are molecules (protein, polysaccharide, etc.) on pathogens that bind to complementary receptors on host cells • Allow them to attach to a specific host cell type/tissue • Attach the pathogen to the host • Can be located on:MCB2004 Microbiology for Health Services Exam #3 Study Guide 4 o Glycocalyx: Polysaccahride coating Streptococcus mutans – causes tooth decay o Fimbriae: Escherichia coli – can attach to small intestine o M Protein – Streptococcus pyogenes Helps them resist phagocytosis 14. Know what a bacterial siderophore does Siderophores
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