LABORATORY DIAGNOSTICS OF INFECTIOUS DISEASES
(2 lessons)
Laboratory examinations:
1) standard routine testing, usual screening
2) organ specific tests indicated on the basis of symptoms
3) inner milieu describing tests
4) type and intensity of inflammation detecting tests
5) etiology detecting tests
Ad 1) common and simple tests, e.g. ESR, blood count, urinalysis, in older persons ECG
Ad 2) tests described in internal propedeutics, examples:
cough
lungs examination chest X-ray
icterus (jaundice)
liver examination
serum liver enzymes and bilirubin, urine
bilirubin and urobilinogen, liver and biliary tact
USG
etc.
Ad 3) tests used in various medical specialties, will be later discussed in intensive care
It is not true that inner milieu testing = blood gases and acid-base balance (Astrup).Blood gases
and acid-base tests belong to extended spectrum of tests:
Situation
general alteration;
preexisting organ disease
dyspnea, disturbed pulmonary
function;
hypotension, cardiovascular
failure;
hemorhagic signs;
multiple organ failure
Testing appropriate
routine:
 blood count
 glycaemia, serum ions (Na, K, Cl)
 serum urea, creatinine
 urinalysis
 serum AST, ALT
extended:
 peripheral blood oxygen saturation (pulse oxymeter)
 pH and blood gas tests (Astrup)
 coagulation tests
 serum albumin
Ad 4) hematological, biochemical and pathological testing detecting type of infection
- blood count and differential count of leukocytes
- pyogenic, suppurative infections: leukocytosis, left shift (immature neutrophilic
polymorphonuclears – bands, possibly metamyelocytes), cytoplasmic granulation of
neutrophils, absence of eosinophils
- intracelular pathogens: decreased number of PMNs, increased lymphocytes and
monocytes
- increased eosinophils: allergy, tissue helmintoses
- CRP and other acute phase proteins
- erythrocyte sedimentation rate (ESR)
Dynamics of inflammatory parameters in the course of bacterial infection.
Ad 5) microbiology diagnostics and clinical interpretation
a) Direct methods of pathogen identification
- microscopy: light, electron, ...
- culture: aerobic vs. anaerobic, on selective media, ...
- antigen detection: clearview, latexagglutination, ....
- molecular genetic methods: PCR, genetic probes, ...
Method
microscopy
culture
antigen detection
specific genome
detection
Contribution
morphology and
number of microbes in
sample;
microbes-leukocytes
and microbes with each
other interrelationship
features of isolated
agents;
complete identification;
sensitivity testing;
storage for future
testing
detects presence of the
searched agent
detects presence of the
searched agent
Advantages
quick, easy,
cheap; low
demands on
equipment
easy, cheap;
low
demands on
equipment
easy, cheap,
quick; low
demands on
equipment
quick; high
sensitivity
Disadvantages
inappropriate in processing of
high quantity of samples;
good experience needed;
only some microorganisms can
be detected on the basis of
morphology
risk of selective identification
of only some microbes;
danger of laboratory infection;
prolonged testing – some
pathogens grow slowly
low sensitivity; with some
samples also low specificity
expensive;
expensive equipment needed;
easy contamination
b) Indirect methods of pathogen identification
- serology: agglutination, hemagglutination, hemagglutination inhibition,
complementfixation, enzyme-linked immunosorbent assay (ELISA), Western blot
etc.
- skin tests: tuberculin test (PPD test, Mantoux II)
- detection of lymphocyte sensibilisation (TB diagnostics)
Method
specific
antibodies
detection
skin tests
Contribution
detects
antibody
response
detects specific
cell-mediated
immunity
Advantages
easy, cheap;
appropriate for
routine processing
easy, very cheap
specific cell-
detects specific more precise, no risk
Disadvantages
inappropriate for identification
of agents with high antigenic
variability
low reliability; risk of allergic
reaction; may induce patient
immunisation – not possible to
repeat
much more expensive than
mediated
immunity
detection
cell-mediated
immunity
of allergy or patient
immunisation
skin test
Serological tests interpretation:
acute infection:
chronic infection:
single sample testing (IgM vs. IgG)
paired sera testing (fourfold elevation of specific antibody titres)
dynamics of antibody titres in time
antibodies avidity testing (the strength of Ab-Ag bind)
Indirect detection methods are based on the detection of specific immune response to infection:
general advantages: can differentiate infection and colonisation
can detect infection that already passed
general limitations: cannot be used in acute and quickly progressing infections (specific immunity
occurs after 1-3 weeks)
not reliable in local infections (e.g. on mucosal surface only)
fail in immunocompromised persons
UPPER RESPIRATORY TRACT INFECTIONS
(1 lesson)
Introduction, pathophysiology
- antiinfective defense of the respiratory tract
- respiratory tract as a continuum, involvement of its parts ranging from nose to trachea
- closely related structures (conjunctiva, paranasal sinuses, middle ear)
- inflammatory edema of respiratory tract mucosa and submucosal lymphatic tissue
Etiology:
- physiological bacterial colonization of the upper respiratory tract
- respiratory viruses: rhinoviruses, coronaviruses, influenza and parainfluenzaviruses, RSV
- pathogenic bacteria:
nasal mucosa: Staphylococcus aureus
nasopharynx: Streptococcus pyogenes, corynebacteria, anaerobes
epiglottis and below: H. influenzae and other gramnegative nacteria
sinuses (sinusitis, otitis): various agents – viruses, bacteria, fungi
Syndromes and etiology:
- acute rhinitis, coryza, common cold: viruses
- acute pharyngitis and tonsillitis: viruses, bacteria
- acute laryngitis: viruses
- acute epiglottitis: H.influenzae
- acute tracheitis: viruses
Complications:
- sinusitis
- otitis media, mastoiditis
- peritonsillar abscess
Separatelly discussed diaseases:
- influenza
- infectious mononucleosis
- diphtheria
Diagnostics, differentiation of viral and bacterial disease:
- inflammatory parameters
- tests for etiology detection - bacterial infection, viral infection
- complementary and syndrome-specific tests
URINARY TRACT INFECTIONS
(1 lesson)
Pathogenesis of urinary tract infections
- route of infection: ascending infection,
hematogenous infection
per continuitatem – very rare
- predisposing factors:
- anatomical factors (short uretra in females, congenital defects...)
- mechanical obstruction from inside (lithiasis, tumours, scarring and postoperative strictures)
and from outside (prostatic hypertrophy, tumours, pregnancy)
- functional neuromuscular defects (paraplegia, sclerosis multiplex, spina bifida)
- metabolic factors (diabetes mellitus)
- microbial pathogenic factors:
- adherence to uroepithelium, colonisation (hemolytic E.coli)
- biofilm production (catheters, chronic infection)
- tissue invasion
Classification of UTI with regard to etiology and pathogenesis:
- community-acquired UTI
- cystitis, pyelonephritis – E.coli, Proteus mirabilis
- urethritis, prostatitis – Mycoplasma, Chlamydia, Neisseria gonorhoae
- chronic UTI in diabetic patients
- besides Gramnegative bacilli frequently Enterococcus
- hospital-acquired UTI
- commonly associated with permanent catheterisation or endoscopy (cystoscopy)
- etiology: multiresistant Gramnegative bacilli (Pseudomonas, Enterobacter, Klebsiella)
Examination procedure
- physical examination
- laboratory testing:
- inflammatory parameters (blood count + differential count of leukocytes, CRP)
- biochemical testing of urine, urine culture
- blood culture if pyelonephritis suspected
- renal function testing (urea, creatinine in serum
- imaging techniques: ultrasonography mostly sufficient
Clinical classification of UTI
Upper urinary tract infection (easy progression to sepsis)
- acute pyelonephritis and chronic pyelonephritis
- interstitial nephritis
- renal absces, pararenal absces
Lower urinary tract infection
- cystitis
- urethritis
- prostatitis
Treatment of UTI
- symptomatic therapy, fluid intake
- antibiotic therapy
CENTRAL NERVOUS SYSTEM INFECTIONS
(1 lesson)
Classification of CNS infections, terminology:
• structure most involved: meningitis, encephalitis, myelitis, radiculitis, neuritis
 type of inflammation: purulent x nonpurulent, aseptic
 pathogen: bacterial, viral, fungal, parasitic
 extent of inflammation:
difusse - meningitis, meningoencephalitis, encephalitis
focal – necrotising encephalitis (HSV), cerebritis, abscess
 course of disease: acute x chronic
Pathogenesis:
- invasion of CNS
- via blood (blood-brain, blood-cerebrospinal fluid barrier)
- via direct spreading from adjacent structures
- via peripheral nerves
- response of CNS to bacterial and viral invasion
- brain edema
Clinical manifestations and etiology of CNS infections:
- meningeal syndrome (headache, vomitus, meningeal signs), fever, coma
- examination of meningeal signs
- symptoms of encephalitis
- purulent meningitis
- clinical presentation
- etiology (pneumococcus, meningococcus, listeria, other agents)
- aseptic meningitis, meningoencephalitis
- clinical presentation
- etiology (tick-borne encephalitis, respiratory viruses, borrelia, leptospira)
Diagnostics:
- diagnosis of CNS inflammation and type of inflammation
lumbar puncture, cerebrospinal fluid testing and findings
- detection of etiology – dirrect and indirrect methods
Basic principles of treatment:
- causative therapy
- symptomatic therapy (including brain edema therapy)
- risk of delayed diagnosis (meningococcal invasive disease, purulent meningitis,
necrotising encephalitis)
IMPORTED INFECTIONS
(1 lesson)
Basic features of imported diseases
- infections of cosmopolitan occurrence
- infections limited to tropical and subtropical climate
Danger:
delayed diagnosis
risk of spreading
Diseases obligatory reported to WHO: variola, cholera, plague, haemorhagic fevers, SARS
The most important syndromes in imported diseases:
fever:
malaria, typhoid fever, dengue fever, haemorrhagic fevers, amebiasis
diarhea:
food-poisoning
bacterial etiology (except pathogens common in middle Europe):
enterotoxigenic E. coli (ETEC), shigellae, V. cholerae
parasitic etiology: Entamoeba histolytica, Giardia intestinalis, Trichuris
trichuria, Ancylostoma duodenale
icterus:
viral hepatitis (A,E,B), yellow fever
leptospirosis
amebic liver abscess, echinococcosis, schistosomosis
exanthema: disesases eliminated by vaccination in developed countries (measles, rubella)
diseases limited to tropical and subtropical climate (dengue, rickettsiosis,
haemorrhagic fevers, larva migrans cutanea)
Examination of traveller:
history including detailed travell history
physical examination, „dominant symptom“
laboratory tests: basic screening + special tests with respect to the suspected diagnosis
Malaria
endemic area
malaric plasmodia: Plasmodium vivax, ovale, malariae, falciparum
life cycle of plasmodium, insect vector (Anopheles mosquito)
clinical manifestation: attack of fever
fever patterns – tertian, quartan, tropical (falciparum) malaria
danger of falciparum malaria
diagnostics: microscopy - thick smear, thin smear of blood
treatment and prevention, increasing resistance to antimalarial drugs
EXANTHEM OF INFECTIOUS ORIGIN
(2 lessons, slide show)
Introduction, terminology:
exanthem (skin), enanthem (mucosal surfaces)
infectious diseases with exanthem as an obligatory symptom and facultative symptom
pathogenesis of exanthem
Examination of patient with rash:
morphological classification of the rash, distribution, pattern of progression, timing
history: vaccination, travelling abroad, known allergy
morphologic types of skin lesions: macula, papula, nodule, vesicle, bulla, pustula
Morphologic classification of exanthems, representative diseases:
1. macular and/or papular exanthem:
scarlet fever (scarlatina)
measles (rubeola, morbilli)
German measles (rubella, rubeola)
Fifth disease (erythema infectiosum)
Sixth disease (exanthema subitum, roseola infantum)
dif. dg. allergic reaction
2. vesicular and pustular exanthem:
generalized: chickenpox (varicella)
smallpox (variola)
localized:
herpes zoster
herpes simplex
impetigo
3. petechial purpuric eruptions:
rickettsiosis – purpuric fever
infections associated with disseminated intravascular coagulopathy:
meningococcal invasive disease
viral hemorrhagic fevers
severe sepsis
Falciparum malaria