Lesson 9Nosocomial Infections

“Healthcare-Related Infections”

March 19, 2015

Hospital Acquired Infections(Nosocomial Infections)

• Nosocomial infections—are infections whose development is favored by a hospital environment– Acquired by a patient during a hospital visit – Infections developing among hospital staff

Centers for Disease Control and Prevention Statistics

• CDC estimates that 1.7 million people acquire infections during their hospital stay– Affects between 5-15% of all hospital patients

• Roughly 100,000 deaths are associated with nosocomial infections– ~36,000 via pneumonia– ~31,000 via bloodstream infections– ~13,000 via urinary tract infections– ~9,000 via surgical site infections– ~11,000 via infections of other sites

• The term nosocomial infections has been updated to health care-associated infections to include other care-giving places– Same day surgical centers– Ambulatory outpatient health care clinics– Nursing homes– Rehabilitation facilities– In-home health care environments

• Joseph Lister developed antiseptic surgical practices and techniques. (Father of Modern Surgery)– Utilized phenol to sterilize equipment– “Scrubbing In”

• Greatly reduced the rate of nosocomial infections (commonly known as “ward fever”)

• In spite of the advances of sterilization techniques, the rate for nosocomial infection has increased in the past 20 years– What could account for this increase in infections in spite of

increased sterilization practices?

• Nosocomial infections are the result of three major factors1. Microorganisms being present in the hospital

environment2. Compromised status of the host 3. Chain of transmission

Microorganisms in the Hospital

• Although typically sterile, the hospital can serve as a reservoir for several pathogens– Normal microbiota of the human body act as

opportunistic pathogens to other patients• Compromised immune systems• Therapy that affect normal function (antibiotics killing

natural flora)

– Most nosocomial infections are caused by human microbiota!!!!

• Nosocomial infections are mostly caused by a fungal or bacterial pathogen– S. aureus (most frequent cause of pneumonia)– Enterococcus spp. (Surgical wound infections)– E. coli (Pneumonia and surgical wound infections)– P. aeruginosa (Pneumonia and surgical wound

infections)– Candida albicans (Urinary tract infection and

sepsis)

• The causative agents of hospital acquired infections have cycled through the years– During the 40-50’s, the most nosocomial infections were

caused by gram (+) microbes• S. aureus

– In the 70’s gram (-) rods were the predominant cause of nocosomial infections

• E. coli and Pseudomonas aeruginosa

– 1980’s antibiotic-resistant strains of gram (+) microbes were predominant

• S. aureus• Enterococcus spp.

Antibiotic Resistance

• Antibiotic resistance has become a major concern regarding nosocomial infections– Organisms that are resistant to more than one

antibiotic is referred to as a multi-drug resistant bacteria (MDR)

– Resistance comes from repeated exposure of a microbe to antibiotics

• “More you use antibiotics; more resistance will form”1. Spontaneous mutation of bacterium’s genome2. DNA transfer from a antibiotic resistant bacterium to a

antibiotic susceptible gene

• Bacterial genomes mutate naturally– A subset of the bacterial population will develop

resistance to antibiotics

– Those not killed are now free to multiply without any competition from the sensitive strains.

• DNA transfer also confers a bacteria with antibiotic resistance

• DNA can be transferred to bacteria via three mechanisms– Conjugation—transfer of bacterial DNA via direct

contact or through an appendage (sex pili)

Conjugation

• DNA transfer also confers a bacteria with antibiotic resistance

• DNA can be transferred to bacteria via three mechanisms– Conjugation—transfer of bacterial DNA via direct

contact or through an appendage (sex pili)– Transduction—transfer of bacterial DNA via

viruses (bacteriophages—viruses that infect bacteria)

Transduction

• DNA transfer also confers a bacteria with antibiotic resistance

• DNA can be transferred to bacteria via three mechanisms– Conjugation—transfer of bacterial DNA via direct

contact or through an appendage (sex pili)– Transduction—transfer of bacterial DNA via viruses

(bacteriophages—viruses that infect bacteria)– Transformation—direct uptake of bacterial DNA

through the cell membrane

Transformation

Affects of Antibiotics

• Antibiotics can also wipe out “friendly” bacteria, which would otherwise compete with the resistant strain for resources.

• Increase resistance in harmless bacteria which can, under certain conditions such as in an immune suppressed patient, become aggressive and cause infection.

Percentage of Total Infections

Percentage Resistant to Antibiotics

Coagulase-negative staphylococci

15% 89%

S. aureus 15% 80%

Enterococcus 10% 4–71%

Gram-negative rods 15–25% 3–32%

C. difficile 13% Not reported

Nosocomial Infections and Their Antibiotic Resistance

Compromised Host

• Compromised host—a person whose resistance to infection is impaired– Disease– Therapy– Injury

• Two principal conditions that compromises the host– Broken skin/mucous membranes– Suppressed immune system

• Skin and mucous membranes function as a physical barrier to pathogens– Compromise to this barrier allows the pathogen to

enter the body• Burns, wounds, and trauma when a patient checks in• Injections, invasive diagnostic procedures, intravenous

therapy, urinary catheters

– Pathogens can proliferate on medical devices• Results from inadequate cleaning of medical

equipment

• Patients that are immunocompromised are at a higher risk in contracting a hospital-acquired infection– Healthy individuals have T cells (T lymphocytes) that directly

kill the bacteria– B cells (B lymphocytes) develop antibodies that ward off

infections• A weakened response to the pathogen allows the

pathogen to grow and proliferate at rapid rates• Drugs, radiation therapy, steroid therapy, burns, diabetes,

leukemia, kidney disease, stress, and malnutrition all contribute to a weakened immune system

Chain of Transmission

• There are two principal routes of transmission of hospital-acquired infections1. Direct contact from health-care provider to

patient or patient to patient contact2. Indirect contact transmission through fomites or

ventilation system (airborne transmission)

• Person-to-person contact– Hospital personnel can transmit microbes to a

patient when changing dressing (wound care)• Transmission via fomites

– Kitchen workers carrying Salmonella, can transmit it to the patient’s food

– Medical equipment can serve as fomites• Urinary catheters• Needles• Respiratory aids (ventilators)

Microorganisms in hospital environment

Chain of transmission

Nosocomial infection

Compromised host

Prevention of Nosocomial Infections

• Hospitals implement different techniques in an effort to control nosocomial infections– Sterilization of equipment

• Disinfecting is not sufficient

– Proper Protective Equipment• Aprons, face shields, gloves

– Surface Sanitation• Touch surfaces common vehicle of pathogen transmission• Implementation of antimicrobial surfaces (usage of Copper)

– Handwashing• According to the CDC, hand-washing is the single most important

means of preventing the spread of infection

Emerging Infectious Diseases

• Diseases that are new, increasing in incidence, or showing a “potential” to increase in incidence in the near future are labeled as Emerging Infectious Diseases– Roughly 75% of emerging diseases are zoonoses and

are mainly viral in origin– Variety of factors that contribute to the emergence of

new infectious diseases

Emerging Infectious Diseases

• Contributing factors– Genetic recombination

• E. coli O157, avian influenza (H5N1)

– Evolution of new strains• V. cholerae O139

– Inappropriate use of antibiotics and pesticides• Antibiotic-resistant strains

– Changes in weather patterns/climate• Hantavirus

Emerging Infectious Diseases

• Modern transportation (traveling)– West Nile virus, Ebola, MERS (middle eastern respiratory

syndrome)• Ecological disaster, war, and expanding human

settlement– Spread of V. cholera after earthquakes in Haiti

• Animal control measures– Over population of reservoirs (deers, raccoons, nutria rat)

• Public health failure– Failure of adults to get proper vaccination

EPIDEMIOLOGY

• Epidemiology—The study of where and when diseases occur and how they are transmitted in populations

• Epidemiologists uses three basic types of investigations when analyzing the occurrence of a disease– Descriptive– Analytical– Experimental

• Descriptive: collection and analysis of data– Retrospective—looking “backward” after the

episode has ended• Ex. John Snow looking for the cause of the cholera

outbreak in London in 1849 (water pump)– Prospective—looking “forward” to see if disease

develops• Epidemiologist looks at a disease-free group and

monitors there habits to see if disease occurs

• Analytical: analyzes a particular disease to determine its probable cause– Case control method—epidemiologist looks for factors that

might have preceded the disease• Age• Sex• Socioeconomic status• Location

– Cohort method—group of people who have the disease is compared to a group that is disease-free

• Comparison of one group of people who have received blood transfusions vs. a group that has not received blood transfusions. (incidence of hepatitis B virus)

• Experimental: experiments to test the hypothesis regarding the characteristics of a particular disease– Assumed effectiveness of a drug

• Experimental drug vs. placebo (substance that has no effect)

Epidemiology

• Centers for Disease Control and Prevention (CDC)– Collects and analyzes epidemiological information in

the United States– Publishes Morbidity and Mortality Weekly Report

(MMWR) – www.cdc.gov

The CDC

• Morbidity: incidence of a specific disease• Mortality: deaths from notifiable diseases

– Notifiable diseases are diseases that are required to be reported to the government by law

– http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6053a1.htm

• Morbidity rate: number of people affected in relation to the total population in a given time period

• Mortality rate: number of deaths from a disease in relation to the population in a given time