Diagnosis by Organ System

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Diagnosis by Organ System
Bloodstream Infections
Microorganisms present in blood, where
continuously, intermittently, or transiently, are
a threat to every organ in the body. Microbial
invasion of the bloodstream can have seriously
immediate sequences , including shock, multiple
organ failure, disseminated intravascular
coagulation (DIC), death. About 200,000 cases
of bacteremia fungemia occur annually, with
mortality rates ranging from 20 - 50.
Causes All major groups of microbes can be
present in the bloo stream during the course of
many diseases. Bacteria, Fungi, Parasites,
Viruses. Types of Bacteremia Bacteremia may be
transient, continuous, or intermittent.
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Types of Bloodstream Infections 1-
Intravascular Those that originate within the
cardiovascular system. A- Endocarditis. B-
Mycotic aneurysm C- Suppurative
thrompophlepitis. D- Intravenous
catheter-associated bacteremia. 2-
Extravascular Those that result from bacteria
entering the blood circulation through the
lymphatic system from another site of infection.
Most cases are a result of extravascular
infection. The common portals of entry for
bacteremia are most 1- The genitourinary tract
(25). 2- Respiratory tract (20). 3- Abscesses
(10). 4- Surgical wound infections (5). 5-
Biliary tract (5). 6- Miscellaneous sites
(10), uncertain sites (25).
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Clinical Manifestations Bacteremia Indicates
the presence of a focus of disease, such as
intravascular infection, pneumonia, or liver
abscess, or transient release of bacteria into
bloodstream. Septicemia or sepsis Indicates a
situation in which bacteria or their products
(toxins) are causing harm to the host.
Unfortunately clinicians often use these terms
interchangeably. Symptoms may include fever or
hypothermia, chills, hyperventilation
(abnormal increased breathing that leads to
excess loss of CO2 from the body) subsequent
alkalosis (condition caused by the loss of acid
leading to an increase in pH), skin lesions,
change in mental status, diarrhea. More
serious manifestations include hypotension or
shock, DIC major organ failure. The syndrome
known as septic shock, characterized by fever,
acute respiratory distress, shock, renal failure,
intravascular coagulation, tissue destruction,
can be initiated by either endotoxins or
exotoxins. Septic shock is mediated by activated
mononuclear cells producing cytokines, such as
tumor necrosis factor interleukins.
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Immunocompromised Patients Detection of
Bacteremia Mortility rate associated with
bacteremia ranges from 20 - 50 . 1- Specimen
Collection A- Preparation of the site. B-
Antisepsis. C- Precautions. D- Specimen volume
Adults 10 -20 ml is recommended. Children 1
5 ml. Infants small E- Number of
blood cultures At least 3 blood cultures to
rule out negative results. F- Timing of
collection When there is symptoms, any time. G-
Anticoagulation dilution. H- Blood culture
media additives.
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2- Culture Techniques A- Conventional blood
cultures 1- Incubation conditions. 2- Detecting
growth. 3- Self-contained subculture system. 3-
Lysis centrifugation. 4- Instrument based
systems Bactec systems, BacT/ALERT microbial
detection system, ESP system. 5- Techniques to
detect IV catheter associated infections. 6-
Handling positive blood cultures. 7-
Interpretation of blood culture results. Special
considerations for other relevant organisms
isolated from blood Hacek bacteria Fungi Mycobacte
ria Spirochetes, Mycoplasma hominis,
Bartonella,B6 dependent Streptococci.
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Infections of the Lower Respiratory Tract
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Anatomy Diseases of the Lower Respiratory
Tract 1- Bronchitis. A- Acute usually caused
by viruses. In infants preschool children is
Bordetella pertussis. B- Chronic caused by
bacteria, such noncapsulated strains of
Haemophilus influenzae, Streptococcus pneumoniae
Moraxella catarrhalis. 2- Pneumonia Pathogenesi
s Clinical Manifestations Community-Acquired
Pneumonia patients are believed to have
acquired infection outside the hospital
setting. The etiology of acute pneumonias is
strongly dependent on age. More than 80 of
pneumonias in infants children are caused by
viruses, whereas 10-20 of pneumonias in adults
are viral.
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Children Children suffer less commonly from
bacterial pneumonia, usually caused by H.
influenzae, S. pneumoniae, or S. aureus.
Neonates may acquire lower respiratory tract
infections with C. trachomatis or P.
carinii. Young Adults The most common etiologic
agent of pneumonia in adults lt30 years age is
Mycoplasma pneumoniae which is transmitted via
close contact. Adults Community acquired
pneumonia in adults is most commonly due to
bacterial infections. S. pneumoniae is most
prevalent, causing 80 of all community-acquired
pneumonia. Pneumonia secondary to aspiration of
gasric or oral secretions is common occurs in
the community setting. Hospital-Acquired
Pneumonia It is the leading cause of death among
patients with nosocomial infections (as high as
50 mortality among patients in intensive care
units). The most common etiologic agents include
Klebsiella spp., other Enterobacteriaceae, S.
aureus, anaerobes, S. pneumoniae, P. aeruginosa,
Legionella. Viruses as influenza virus,
respiratory syncytial virus, adenovirus.
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Chronic Lower Respiratory Tract
Infections Mycobacterium tuberculosis is the most
likely etiologic agent of chronic lower
respiratory tract infection, but fungal infection
anaerobic pleuropulmonary infection may also
run a subacute or chronic course. Cystic
fibrosis (CF) is a genetic disorder that leads to
persistent bacterial infection in the lung,
causing airway wall damage chronic obstructive
lung disease. Immunocompromised Patients Patients
with neoplasm Transplant recipients HIV-infected
patients Pleural Infections Laboratory Diagnosis
of Lower Respiratory Tract Infections Specimen
Collection Transport Sputum, transtracheal
aspirate, bronchial washings. Specimen
Processing Direct visual Examination Routine
Culture
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Upper Respiratory Tract Infections Other
Infections of the Oral Cavity
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Laryngitis Caused almost exclusively by
viruses. Laryngotracheobronchitis or
Croup Viruses a primary cause of
croup. Epiglottitis Is usually caused by
bacteria. Haemophilus influenzae type b is the
primary cause of epiglottitis. Other organisms
occasionally implicated are streptococci
staphylococci. Pharyngitis tonsillitis Pharyngit
is (sore throat) tonsillitis are common upper
respiratory tract infections affecting both
children adults. Clinical Manifestations Affecte
d tissues are erythematous swollen with pain.
Depending on the causative organism, either
inflammatory exudates (fluid with protein,
inflammatory cells, cellular debris), vesicles
(small blister like sacs containing liquid)
mucosal ulceration, or nasopharyngeal lymphoid
hyperplasia (swollen lymph nodes) may be
observed.
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Etiologic agents Most cases of pharyngitis occur
during the colder months often accompany other
infections, primarily those caused by
viruses. Although different bacteria cause
pharyngitis tonsillitis, the primary cause is
Streptococcus pyogenes. Although H. influenzae,
S. aureus, S. pneumoniae are frequently
isolated from nasopharyngeal throat cultures,
they have not been shown to cause
pharyngitis. Vincent's angina or anaerobic
tonsillitis, involves pseudomembrane formation on
tonsillar surfaces. Multiple anaerobes,
especially Fusobacterium necrophorum are
implicated in this syndrome. Gram stain reveals
numerous fusiform, gram-negative bacilli
spirochetes. Peritonsillar Abscesses Caused by
non-spore-forming anaerobes, including
Fusobacterium, Bacteroides, anaerobic cocci.
S. pyogenes viridans streptococci may also be
involved. Rhinitis (common cold) Inflammation of
nasal mucous membrane or lining. It is caused by
viruses.
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Miscellaneous Infections Caused by Other
Agents Corynebacterium diphtheriae Bordetella
pertussis Klebsiella spp. Rhinoscleroma is a rare
form of chronic, granulomotous infection of the
nasal passages, including the sinuses
occasionally the pharynx larynx. Associated
with K. rhinoscleromatous, the disease is
associated with nasal obstruction caused by
tumorlike growth with local extension. K.
Ozaenae may contribute to another infrequent
condition called ozena, characterized by a
chronic, mucopurulent nasal discharge that is
often foul-smelling. It is caused by secondary,
low-grade anaerobic infection. Oral
Cavity Stomatitis Herpes simplex virus agent of
the disease, in which multiple ulcerative lesions
are seen on the oral mucosa. is the primary.
Thrush Caused by Candida spp.
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Periodontal Infections It involves anaerobes,
Streptococci, Staphylococci Eikenella
corrodens. Salivary Glands Infections Staphylococc
us aureus is the major pathogen, but viridans
streptococci anaerobes may play a role. Mumps
virus Neck Diagnosis of the Upper Respiratory
Tract Infections Collection Transport of
Specimens Dacron, cotton, or calcium
alginate-tipped swabs are suitable for collecting
most upper respiratory tract microorganisms.
Moist swabs can remain for 4 hours, otherwise
transport medium is needed S. pyogenes is an
exception as it remains for 48-72 hours viable in
dry swabs. Nasopharyngeal swabs are suitable for
detecting other bacteria viruses (Bordetella
pertussis, Neisseria spp.) Direct Visual
Examination Gram stain is of little help. 10
KOH for fungi
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Culture Streptococcus pyogenes Corynebacterium
diphtheriae Bordetella pertussis Neisseria Epiglot
titis Noncutlure Methods for Detection of S.
pyogenes in Throat Specimens. Diagnosis of
Infections in the Oral Cavity Neck Collection
Transport Direct Visual Examination Culture
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Meningitis Other Infections of the CNS
Anatomy An understanding of the basic anatomy
physiology of the CNS is helpful for the
microbiologist to ensure appropriate specimen
processing interpretation of laboratory
results. Coverings spaces of the CNS 1- Bone
outercovering of the brain the spinal cord. 2-
Inner covering of membranes called meninges which
are of 3 layers surrounding the brain the
spinal cord. These are A- Dura mater B-
Arachnoid C- Pia mater The last 2 are
collectively called leptomeninges. Between
around the meninges are spaces that include the
epidural, subdural, subarachnoid spaces.
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Cerebrospinal Fluid Routes of Infection Diseases
of the CNS Meningitis Infection within the
subarachnoid space or throughout the
leptomeninges is called meningitis. It is
divided into 2 major categories 1- Purulent
Meningitis Bacteria usually cause these
infections. Clinical Manifestations Acute Chronic
Etiologic Agents It is very dependent on the age
of the patient. H. Influenzae is the most
etiologic agent in children between 1 month 6
years. About 95 of the cases are caused by Hib,
S. pneumoniae, N. meningitidis.
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Neonates are likely to be infected by S.
agalactiae, E. coli, other gram negative
bacilli Listeria monocytogenes. Occasionally
other organisms are involved, Chrysobacterium
meningosepticum. In adults N. meningitidis, S.
pneumoniae,, S. aureus various gram negative
bacilli. 2- Aseptic Meningitis Commonly
associated with viral infection. Encephalitis/Meni
ngoencephalitis An inflammation of the brain
parenchyma is usually a result of viral
infection. Brain Abscess Laboratory
Diagnosis Meningitis Specimen collection
Transport CSF is collected aseptically by
inserting a needle into the subarachnoid space at
the level of the lumbar spine. A minimum of 5-10
ml should be collected. .
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Specimen should be delivered immediately to the
laboratory. Specimen should not be refrigerated.
If specimen is not processed immediately, it
should be incubated at 35c or left at room
temperature. Initial Processing Microbiology 1-
Direct stained smear 2- Wet preparation 3- India
ink stain 4- Direct Detection of etiologic
agents. 5- Culture Cytology Total cell count
differential. Biochemistry Glucose protein
level.
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Infections of the Eye, Ear Sinuses
Eye Anatomy Resident Microbial Flora Staphylococcu
s epidermidis, Lactobacillus spp. are the most
frequently encountered organisms,
Propionibacterium acnes, S. aureus, H.
influenzae, Moraxella catarrhalis,
Enterobacteriaceae various Streptococci. Disease
s Blephritis Conjuncivitis Keratitis Endophthelmit
is Periocular
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Laboratory diagnosis Specimen Collection
Transport Purulent material from the surface of
the lower conjunctival sac inner canthus
(angle) of the eye is collected on a sterile swab
for culture of conjunctivitis. Both eyes should
be cultured separately. In keratitis, an
ophthalmologist should obtain scrapings of the
cornea with a heat sterilized platinum
spatula. Cultures of endophthalmitis specimens
are inoculated with material obtained by the
ophthalmologist from the anterior posterior
chambers of the eye. Lid infection material is
collected on a swab Direct Visual
Examination Gram stain, DFA Culture Blood agar,
chocolate agar. Incubation under 5-10 CO2 at
37c for 24-48 hors. Noneculture method ELISA,
DFA, PCR for Chlamydia trachomatis viruses.
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Ears
Anatomy Resident Microbial Flora The normal flora
of the external canal are rather sparse, similar
to that of the conjunctival sac
qualitatively. Staphylococcus epidermidis,
Lactobacillus spp. are the most frequently
encountered organisms, Propionibacterium acnes,
S. aureus, H. influenzae, Moraxella catarrhalis,
Enterobacteriaceae various Streptococci. Diseaes
Otitis Externa Otitis Media Laboratory
Diagnosis Specimen Collection Transport
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Ear discharge. Culture Media blood agar,
chocolate agar, MacConkey.
Sinuses
Anatomy Diseases Laboratory Diagnosis Gram
stain Aerobic Culture blood agar, chocolate
agar, MacConkey. Anaerobic Culture
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External ear Middle ear
Inner ear
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Infections of the urinary Tract
Anatomy
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Resident Flora The urethra has resident
microflora the colonize its epithelium in the
distal portion. All areas of the urinary system
above the urethra in a healthy human are sterile.
Coagulase negative staphylococci, diphtheroids,
viridans nonhemolytic streptococci,
lactobacilli, nonpathogenic Neisseria, anaerobic
gram negative cocci bacilli, commensal
Mycobacteria Mycoplasma spp. Infection of the
Urinary Tract Epidemiology Approximately 10 of
humans will have a UTI at some time during their
lives. It is age sex dependent. During the
first year of life UTIs are more common in males.
However, the incidence of UTIs among males is
low after age 1 until approximately age 60 when
enlargement of the prostate interferes with
emptying of the urinary bladder. Therefore UTI is
predominantly a disease of females. Sexual
activity, anatomic hormonal changes 7 pregnancy
favor development of UTIs. Etiologic Agents 1-
Community Acquired 2- Hospital Acquired
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Types of Infections their Manifestations 1-
Urethritis 2- Cystitis 3- Acute Urethral
Syndrome 4- Pyelonephritis Laboratory Diagnosis
of Urinary Tract Infections Specimen
Collection Clean-Catch, Midstream Urine Straight
Catheterized Urine Suprapubic Bladder
Aspiration Indwelling Catheter Specimen
Transport Screening Procedures Gram stain,
pyuria, indirect indices, nitrate reductase,
leukocytes esterase, catalase. Automated systems.
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Urine Culture Inoculation Incubation of Urine
Cultures Interpretation of Urine Cultures
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Gastrointestinal Tract Infections
Anatomy Resident Microbial Flora Gastroenteritis P
athogenesis Host Factors Microbial
factors Toxins Entertoxins Cytotoxins Neurotoxins
Clinical Manifestations
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Other Infections of the GI Tract Esophagitis The
most common etiologic agents are Candida spp.,
herpes simplex CMV. Gastritis Helicobacter
pylori. Procitis Chlamydia trachomatis, herpes
simplex, syphilis, gonorrhea are the most
common etiologic agents. Miscellaneous Laboratory
Diagnosis of Gastrointestinal Tract
Infections Specimen Collection Transport Stool
specimens should be collected in clean plastic
container delivered to the laboratory within
one hour. Stool for toxin assay for Clostridium
difficile, immunoelectron microscopy for
rotavirus, ELISA or latex agglutination for
rotavirus should be sent without preservatives.
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Stool Specimen for Bacterial Culture If a delay
more than 2 hours is anticipated for stools for
culture, the specimen should be placed in
transport medium such as Cary-Blair transport
medium. If stool is not available, a rectal swab
may be substituted as a specimen for bacterial or
viral culture. Stool Specimens for
Viruses Miscellaneous Specimen Types Direct
Detection of Agents of Gastrointestinal Types Wet
Mounts Stains Antigen Detection Molecular
Biological Techniques Culture of Fecal Material
for Isolation of Etiologic Agents Routine Culture
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A
C
E
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Skin, Soft Tissue, Wound Infections
Anatomy of Skin Etiologic Agents
Pathogenesis Many different bacteria, fungi 7
viruses may be involved. Skin Soft Tissue
Infection Skin Infections in or around Hair
Follicles Folliculitis, furnculosis, carbuncles
are localized abscesses either in or around hair
follicles. Staphylococcus aureus is the most
etiologic agent for all three infections. Infectio
ns in the Keratinized Layers of the Epidermis
Because of their ability to utilize keratin in
the cells of the epidermis, hair nails, the
dermatophyte fungi are significant well suited
pathogens for this site. Infections of the Deeper
Layers of the epidermis the Dermis
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Infections of the Subcutaneous Tissues Abscesses,
ulcers boils. S. aureus is the most common
etiologic agent of subcutaneous abscesses in
healthy individuals. Also the etiologic agent
depends on the site of infection. Infections of
the Muscle Fascia Muscles Necrotizing
Fascitis Progressive Bacterial Synergistic
Gangrene Myositis Wound Infections Postoperative
Infections Bites Burns Infections Related to
Vascular Neurologic Problems Sinus Tract
Fistulas Systemic Infections with Skin
Manifestations
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Laboratory Diagnostic Procedures Infections of
the Epidermis Dermis Erysipeloid Superficial
Mycosis Erythrasma Erysipelas
Cellulitis Vesicles 7 Bullae Infections of the
Subcutaneous Tissues Infections of the Muscle
Fascia Muscles Wound Infections Postoperative Bi
tes Burns
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A C
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Normally Sterile Body Fluids, Bone, Bone
Marrow, Solid Tissues
Specimens from Sterile Body Sites Fluids In
response to infection, fluid may accumulate in
any body cavity. Infected solid tissue often
presents as cellulitis or with abscess formation.
Areas of body from which fluids are typically
sent for microbiologic studies in addition to
blood CSF include Pleural Fluid The parietal
pleura, a serous membrane of the thoracic cavity,
lines the entire thoracic cavity. The visceral
pleura lines the lungs. The pleural fluid is
present between the lungs chest wall. It
contains little or no cells is similar to serum
with a lower protein content. Effusion or
transudate is an excess amount of fluid as a
result of cardiac, hepatic or renal disease.
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An exudate , pleural fluid that contains numerous
white blood cells other evident of an
inflammatory response. It is usually caused by
infection, but malignancy, pulmonary infarction
or autoimmune disease may also be
responsible. Thoracentesis, material collected
from the patient by needle aspiration Empyema
fluids, exudative pleural fluid that contain
numerous polymorphonuclear neutrophils, are
grossly purulent. It usually occurs secondary to
pneumonia, but other infections may cause
it. Peritoneal Fluid The peritoneum is a large
moist , continuous sheet of serous membrane that
lines the walls of the abdominal pelvic cavity
the organs within it. The two membrane lining
are separated by the peritoneal cavity. It
contains peritoneal fluid which contains as many
as 300 WBCs/ml. Ascitis, inflammation within the
peritoneal cavity with accumulation of ascitic
fluid Which contains inflammatory cells an
elevated protein level. Primary peritonitis
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Primary Peritonitis No apparent cause of
infection is recognized. The most common
etiologic agents in children are Streptococcus
pneumoniae, S. pyogenes, Enterobacteriaceae,
othergram negative bacilli. In adults,
Escherichia coli is the most common bacterium,
followed by S. pneumoniae S. pyogenes.
Polymicrobic peritonitis is unusual in the
absence of bowl perforation or rupture.
Tuberculous peritonitis also, Neisseria
gonorrhoeae, Chlamydia trachomatis are common
etiologic agents of peritoneal infection in
sexually active women. Secondary Peritonitis Is
equalae to a perforated viscus, surgery,
traumatic injury, loss of bowl wall integrity
because of destructive disease (ulcerative
colitis, ruptured appendix, carcinoma),
obstruction, or a preceding infection.
Anaerobes, Enterobateriaceae, enterococci or
other streptococci, S. aureus. Peritoneal
Dialysis Fluid For end stage renal disease
patients. Such patients are at risk of
peritonitis. Peritonitis is best diagnosed by
the presence of cloudy dialysate with or without
abdominal pain. S. aureus S. epidermidis are
the most common etiologic agents, followed by
streptococci, aerobic facultative anaerobic
gram negative bacilli, Candida, Corynebacterium
spp.
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Pericardial Fluid Agents of pericarditis
myocarditis are usually viruses, bacteria,
certain fungi noninfectious causes. Joint
Fluid S. Aureus is the most common etiologic
agent of arthritis, account for about 70 of such
infections. Also N. gonorrhoeae, H. influenzae,
streptococci, anaerobes. Bone Bone Marrow
Aspiration or Biopsy For diagnosis of
brucellosis, histoplasmosis, bastomycosis,
tuberculosis leishmaniasis. Bone Biopsy S.
aureus is the most etiologic agent of
ostiomyelitis in patients of all age
groups. Other agents such as Salmonella,
Haemophilus, Enterobacteriaceae, Pseudomonas,
Fusobacterium yeast. Parasites viruses are
rarely if ever, etiologic agents of
osteomyelitis. Solid Tissues
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Laboratory Diagnostic Procedures Specimen
Collection Transport Fluids Aspirates Most
specimens (pleural, pericardial, peritoneal
synovial fluids) are collected by aspiration with
a needle syringe. Bone Tissue Specimen
Processing, Direct Examination Culture Fluids
Aspirates Bone Solid Tissue
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Nosocomial Infections
Every year, between 1.75 3 million (5 to
10)of the 35 million patients admitted to acute
care hospitals in the united states acquire an
infection that was neither present nor in the
prodromal (These infection) stage when they
entered the hospital. These infections are
called nosocomial or hospital- acquired,
infections. Treatment of these infections is
estimated to add between 4.5 15 billion
annually to the cost of health care. In
addition, many of these infections lead to the
death of hospitalized patients (patient
mortality) or at minimum, lead to additional
complications (patient morbidity) antimicrobial
chemotherapy. Incidence of Nosocomial
Infections The most common nosocomial infections
are 1- Urinary tract 33. 2- Pneumonia 15. 3-
Surgical sites 15. 4- Blood stream 13.
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Each nosocomial infection adds 5-10 days to the
affected patient hospital stay. Of individuals
with hospital acquired bloodsteam or lung
infections, 40 to 50 die each year. Likewise,
patients with indwelling (Foley) catheters have a
threefold increase chance of dying from
urosepsis, a bloodstream infection that is a
complication of a urinary trat infection, than
those who do not have one. Within hospitals, the
surgical medical services have the highest
rates of infection, the pediatrics nursing
services have the lowest. Moreover within
services, the predominant type of infections
varies, that is, surgical site infections are the
most common on the surgical service while urinary
tract or bloodstream infections are the most
common on medical services or the nursery. Types
of Nosocomial Infections The majority of
nosocomial infections are endogenous, that is
they involve patients own microbial flora. In
general hospitalized individuals have increased
susceptibility to infection. Corticosteroids,
cancer chemotherapeutic agents, antimicrobial
agents all contribute to the likelihood of
nosocomial infection by suppressing the immune
system or altering the host normal flora to that
of resistant (hospital) microbes.
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Foreign objects such as catheters, needed for the
care of the patients, break the body's natural
barriers to infection. Also it is not possible
to immunize patients to nosocomial infections.
Patients admitted to the hospital with serious
community acquired infections may spread the
infection by food, water, medications or medical
devices, or by airborne transmission. Thus
nosocomial infections may never be eliminated ,
only controlled. Urinary Tract Infection Gram
negative rods cause the majority of hospital
acquired urinary tract infections, Escherichia
coli is the number one organism involved. Gram
positive organisms, Candida spp., other fungi
cause the reminder of the infections. Lung
Infections The most common nosocomial pathogens
causing pneumonia are gram negative rods, S.
aureus, Moraxella catarrhalis, Streptococcus
pneumoniae Haemophilus influanzae, which cause
the majority of community acquired pneumonias,
are not important etiologic agents of hospital
acquired infections except very early in
admission as they are present before.
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Surgical Site Infections Approximately 4 of
surgical patients develop surgical site
infection, 50 of which develop after the patient
has left the hospital so this number may be an
underestimate. Gram positive organisms (S.
aureus coagulase negative staphylococci
enterococci) cause the majority of these
infections followed by gram negative rods
Candida spp. Bloodstream Infections Emergence of
Antibiotic-Resistant Microorganisms The organisms
that cause nosocomial infections have changed
over the years because of selective pressures
from the use overuse of antibiotics. Risk
factors for the acquisition of highly resistant
organisms include prolonged hospitalization
prior treatment with antibiotics. Patients normal
flora changes very quickly after hospitalization
to potentially resistant microorganisms found in
the hospital environment. These patients serve
as potential reservoirs for spread to other
patients.
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Hospital Infection Control Microorganisms are
spread in hospitals through several modes 1-
Direct contact, for example in contaminated food
or intravenous solutions. 2- Indirect contact,
for example, from patient to patient on the hands
of health care workers. 3- Droplet contact, by
inhalation of droplets. 4- Airborne contact,
inhalation of droplets that can travel distances
on air currents (tuberculosis). 5- Vector borne
contact, disease spread by vectors such as
mosquitoes or rats. Thus when the reservoir is
known, control measures can be taken. Role of
Microbiology Laboratory
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• Characterizing Strains Involved in an Outbreak
• 1- Classic Phenotypic Technique it includes
• Biotyping (analyzing biologic or biochemical
  characteristics).
• Antibiogram (antibiotic susceptibility).
• - Serotyping ( serologic typing.
• - Bacteriocin typing.
• Bacteriophage typing.
• 2- Genotypic or Molecular Methods
• Plasmid analysis restriction endonuclease
  analysis of chromosomal DNA.
• Preventing Nosocomial Infections
• Surveillance Cultures