Principles of Disease and Epidemiology

Ch 14

Diseases and US

• Pathogen : a disease causing microbial growth or toxin.

• Disease: an abnormality in which the body or part is not properly adjusted. The body part is overcome by the microbe– Change in the state of health

• Infection: is the invasion and growth of a pathogen in the body

More words

• Host: Is an organism that shelters and supports the growth of pathogens.

• Pathology: scientific study of disease

• Etiology: cause of a disease

• Pathogenesis: development of disease

• Is this a type of symbiosis?

Normal Microbiota

• In some cases it is normal for microbes to be growing.

• Most mammals germ free in utero, are colonized after birth.

• Microbes that establish permanent colonies inside or on outside of the body without causing disease are called normal microbiota.

• Transient microbiota are microbes that are stable for a time then disappear.

Symbiosis

• With normal microbiota, usually both species benefit from this arrangement.

• Normal microbiota can prevent infections, may make necessary vitamins in return for nutrients form the host. (is called…..

• Opportunistic microbes may cause disease under certain instances.

• Probiotics are live microbes applied to or ingested into the body, intended to exert a beneficial effect.

Normal Microbiota on the Human Body

Table 14.1

Skin

• Propionibacterium acnes

• Staphylococcus epidermidis

• Staphylococcus aureus

• Candida spp

• Most microbes are transient on skin.

• Why?

Eyes

• Basically the same as that found on the skin.

• Eyes have lysozyme, few nutrients, washing by tears.

Nose and throat

• S. aureus• S. epidermides

• Streptoccoccus pneumoniae

• Haemophilus• Neisseria

Mouth

• Streptoccoccus• Lactobacillus• Actinomyces• Bacteroides• Fusobacterium• Treponema• Cornebacterium• Candida• Over 200 species

• Idea environment• Is a diverse

environment.

• How do we know what lives in the mouth?

Large intestine• Bacteroides• Fusobacterium• Lactobacillus• Enterococcus• Escherichia• Enterobacter• Proteus• Klebsiella• Shigella• Candida

• Is essentially a chemostat

• Has a large resident microbiota

Urogenital system

• Staphylococcus epidermidis

• Enterococcus• Lactobacillus• Pseudomonas• Klebsiella• Proteius• In urethra

• Lactobacilli• Streptococcus• Staphylococcus• Bacteroides• Clostridium• Candida albicans• Trichomonas

vaginalis• in vagina is acidic

Koch’s postulates

• Same pathogen must be present in every case of the disease

• Pathogen must be isolated in pure culture

• Pathogen isolated from pure culture must cause the same disease in a healthy, susceptible laboratory animal.

• Pathogen must be isolated from this animal

Exceptions to Koch’s postulates

• Are modified to establish etiologies of diseases caused by viruses and fastidious bacteria, which cannot be grown on defined media.

• Some diseases are caused by a variety of microbes.

• Some diseases such as S. pyogenes can cause several different diseases.

• Some diseases can only occur in one organism so we cannot run the full Koch’s postulates.

• Why?

Disease classification and codification

• Vocab

• Measurements

• Recognition and patterns

• Symptoms- change in body function• Diagnosis- identification• Sign- a measurable change• Syndrome- a specific group of symptoms

or signs that always accompanies a specific disease.

• Communicable diseases- transmitted directly or indirectly from one host to another.

• Contagious disease- is easily spread from one person to another

• No communicable diseases- are caused by microbes that normally grow outside the body and are not transmitted from one host to another– Clostridium tetani

Where, how bad and how much. Words to describe ID

• Incidence- number of people contracting the disease

• Prevalence- number of cases at a particular time

• Frequency- is in terms of sporadic, endemic, epidemic and pandemic

• Acute, chronic, subacute and latent• Herd immunity- is the presence of

immunity in most of the population

• Local infection- affects a small area of the body

• Systemic infection- spread throughout the body– Bacteremia- bacteria in the blood– Septicemia- bacteria multiply in blood

• Secondary infections- occur after a host is weakened from a primary infection

• Subclinical- cannot be measured

• Acute disease Symptoms develop rapidly• Chronic disease Disease develops

slowly• Subacute disease Symptoms between acute

and chronic• Latent disease Disease with a period of no

symptoms when the patient is inactive

Severity or Duration of a Disease

Recognition and patterns of disease

• Predisposing factors make the body more susceptible to disease they include– Gender– Climate– Age– Fatigue– Nutrition– Lifestyle– Drug treatments

What happens when a disease does occur?

• Incubation period- is the time between the initial infection and the first appearance of signs and symptoms

• Prodromal- period is the first mild signs and symptoms

• Illness- is when the disease is at its height

• Decline- signs and symptoms decline

• Convalescence- time until the body returns to predisease state

The Stages of a Disease

Figure 14.5

Spreading of Infection

• Reservoir of infection – provides pathogen with conditions for survival– Human – carriers, asymptomatic or latent– Animal- zoonoses various routes– Nonliving Reservoirs – water, fertilizer ect

Transmission of Disease

• Contact transmission– Direct person to person transmission

• Indirect contact transmission– Fomite a nonliving transfer (1 meter, soiled

goods)

• Droplet transmission over short distances

• Vehicle transmission (water, food, air)

• Vectors (mechanical or biological)

Transmission of Disease

Transmission of Disease

Figure 14.6a & 8

Portals of entry and Exit

• Pathogens have preferred portals of entry and exit.

• Most common portals– Respiratory tract– Gastrointestinal tract– Urogenital tract– Blood to blood

• Vehicle Transmission by an inanimate reservoir (food, water)

• Vectors Arthropods, especially fleas, ticks, and mosquitoes

• Mechanical Arthropod carries pathogen on feet

• Biological Pathogen reproduces in vector

Transmission of Disease

Nosocomial (Hospital-acquired) infections

• 5-15% get infections while in the hospital.

• Microbes in hospital

• Chain of transmission

• Compromised host

• Is a hospital the best place to be if you are sick?

Figure 14.7, 9

• Are acquired as a result of a hospital stay

• 5-15% of all hospital patients acquire nosocomial infections

Nosocomial (Hospital-Acquired) Infections

Nosocomial Infections

Table 14.5

ANIMATION Nosocomial Infections: Overview

Percentage of Total

Infections

Percentage Resistant to Antibiotics

Coagulase-negative staphylococci

25% 89%

S. aureus 16% 80%

Enterococcus 10% 29%

Gram-negative rods

23% 5-32%

C. difficile 13% None

Common Causes of Nosocomial Infections

MRSA

• USA100: 92% of health care strains

• USA300: 89% of community-acquired strains

Clinical Focus, p. 422

Which Procedure Increases the Likelihood of Infection Most?

Clinical Focus, p. 422

ANIMATION Nosocomial Infections: Prevention

Control of Nosocomial

• Aseptic techniques– Hand washing (40% compliance)

• Infection control staff

Emerging Infectious diseases

• Ones that are new or changing• Global warming• Global transportation• Antibiotics• Breakdown in social order• Governance problems• Pesticides• Lack of vaccination• Lack of reporting

Epidemiology

• Study of transmission incidence and frequency of disease.

• Data are collected and analyzed in descriptive epidemiology

• Analytical epidemiology- infected comp to uninfected

• Controlled experiments• Case reporting• CDC reporting

• CDC (Centers for Disease Control and Prevention) main source of epidemiologic info in US

• Publishes Morbidity and Mortality Weekly Report, reports incidence and deaths.

• Collects and analyzes epidemiological information in the U.S.

• Publishes Morbidity and Mortality Weekly Report (MMWR) www.cdc.gov

Morbidity: incidence of a specific notifiable disease

Mortality: deaths from notifiable diseases

Morbidity rate = number of people affected/total population in a given time period

Mortality rate - number of deaths from a disease/total population in a given time

Centers for Disease Control and Prevention (CDC)

• The study of where and when diseases occur

Epidemiology

Figure 14.11

New fields of Biological study

• Biological crimes? ASM paper

Nosocomial outbreak (page 445)

• 7 year period 361 patients developed bacteremia

• Burkholderia cepacia identified (same strain)

• Infection within 36hr of IV

• Disappears hrs after IV removed

• Cleaning insertion site

• Iodine is negative

Continued

• Not found in povidone-iodine

• In alcohol

• Alcohol purchase as 90% and diluted in pharmacy.

• Used the same 100l container

• Used the same tap water

• Tap water contaminated

• How do you prevent this from happening?