medical students

1. APPROACH TO
INFECTIOUS DISEASES
PROF DR FARHAT BASHIR
DEPARTMENT OF MEDICINE

2. • DISEASE: a pathological condition of body parts or tissues
characterized by an identifiable group of signs and symptoms.
• INFECTIOUS DISEASE: diseases caused by infectious
agents that can be passed on to others.
• INFECTION: the colonization of a host organism by a
parasitic species. It occurs when an infectious agent enters the
body and begins to reproduce, it may or may not lead to disease.
• INFECTIVITY: the ability of an organism to enter, survive and
multiply in host.
• INFECTIOUSNESS OF DISEASE: indicates the comparative
ease with which the disease is transmitted to other hosts.

3. • PATHOGEN: infectious agent that is capable of causing
disease.
• VIRULENCE: the relative ability of an agent to cause rapid
and severe disease in host.

4. • Infectious diseases are the leading cause of death world wide.
• Responsible for 1/4 -1/3 of all deaths.

5. CLASSIFICATION OF INFECTIOUS
DISEASE
• DURATION
• ACUTE
• CHRONIC
• SUB-ACUTE
• LATENT

6. • EXTENT
• LOCALIZED
• SYSTEMIC
• ORGAN/ORGAN SYSTEM

7. • MANIFESTATION
• SYMPTOMATIC/ CLINICAL
• ASYMPTOMATIC/ SUBCLINICAL

8. • PRIMARY
• SECONDARY

9. AGENTS
• Bacteria
• Virus
• Parasites – protozoa, helminthes
• Fungi
• Prions
SOURCE OF INFECTION!

10. TRANSMISSION
• Air
• Contaminated food/ water
• Body fluids
• Direct contact with contaminated objects
• Animal vectors

11. PHASES OF INFECTIOUS DISEASE
• Incubation period
• Prodromal period
• Illness/ clinical period
• Decline/ defervescence
• Convalescent/ recovery

12. MECHANISM OF PATHOGENECITY
• Production of toxins/ enzymes that destroy cells and tissues
• Direct invasion and destruction of host cells
• Triggering response from host immune system leading to
disease signs and symptoms

13. STEPS IN PATHOGENESIS
• ENTRY
• Penetration of skin or mucus membrane
• Inoculation into body tissues
• Inhalation
• Ingestion
• Introduction
• Use of shared needles
• ATTACHMENT
• MULTIPLICATION
• INVASION/ SPREAD
• EVASION OF HOST DEFENSES
• DAMAGE TO HOST TISSUES

14. CLINICAL FEATURES
• Fever
• Fatigue
• Weight loss
• Night sweats/ chills
• Body aches and pain
• Rash
• Localizing symptoms

15. PREVENTION AND CONTROL
• Vaccines
• Antimicrobials
• Personal hygiene and sanitation
• Vector protection
• Quarantine

16. EMERGING INFECTIONS
• The infections that have recently appeared in a population or
whose incidence is increasing rapidly
• Appearance of previously unknown agent
• Spread to new host
• Spread to new location
• Acquisition of resistance
• Deliberate introduction into a population

17. CLINICALAPPROACH
• History
• Symptoms- fever, rash, localizing symptom, etc.
• Examination (Physiological assessment)
• Signs
• Investigation (Diagnostic assessment)
• Management

18. Case 1
18

19. Chief Complaint:
Fever—1 week
Right upper abdominal pain- 1 week
Vomiting - 2 days
19

20. HISTORY
• History of fever and other presenting complaints
• Systemic review
• Past medical history
• Drug history
• Travel history
• Contact history

21. History of present illness
1 week
-continuous moderate to low
grade fever & right upper abdominal pain
2 days
-vomiting
21

22. • Abdominal pain(+) aching right hypochondrial non-radiating,
relieved slightly on rest, aggravated by eating, anorexia +,
vomiting 4-5 episodes /day, non-projectile, contains food eaten, no
blood, taste sour or bitter, no constipation, no melena, no
hematochezia (-), no diarrhea,
REVIEW OF SYSTEMS:
• No significant weight loss (-)
• No loss of consciousness, no headache (-)
• No blurring of vision (-)
• No ear discharge, no tinnitus (-)
• No cough, no difficulty of breathing (-)
• No chest pain, no palpitation (-)
• No dysuria, no frequency, no urgency, (-)
• No polyuria, no polydipsia, no polyphagia (-)
• No heat or cold intolerance (-)
22

23. Past Medical History
 No other medical or surgical illness requiring
hospitalization
 No history of blood transfusion
 No history of illicit drug use nor maintained on any
medication
 No history of tattoo, piercing
 No history of wading in sewage waters
23

24. Personal History
• Non smoker,
• Non alcoholic
• Lives in endemic areas
24

25. Family History
• No hypertension
• No diabetes mellitus
• No cancer
• No pulmonary tuberculosis
25

26. PHYSICALEXAMINATION FINDINGS
 A young man of average built and physique, well-
oriented in time, place and person
 Pulse 88/minute, regular, normal volume and character,
vessel wall not palpable, all peripheral pulses palpable
 BP - 120/80
 RR - 21
 Temp - 38.5°C
26

27. PHYSICALEXAMINATION FINDINGS
• Height - 1.5m
• Weight - 52.6kg
• BMI - 23
• No skin rashes
• No pallor
• Jaundice +
• No nasal nor aural discharge
• No oral ulcers or sores, dry tongue (+), no dental
caries
• Thyroid gland not enlarged, supple neck, no palpable
cervical lymphadenopathy
27

28. 31
PRESENTING(CHIEF)
COMPLAINT:
FEVER• Fever
• is an elevation of body temperature that
exceeds the normal daily variation and
occurs in conjunction with an increase in
the hypothalamic set point.
• a protective mechanism of the body

29. 32
Requirements for the Induction of Fever
Infection, microbial toxins, mediators
of inflammation, immune reactions Microbial toxins
FEVER
Monocytes/macrophages,
endothelial cells, others
Pyrogenic cytokines IL-1, IL-6,
TNF, IFN
Cyclic
AMP
PGE₂
Hypothalamic
endothelium
Elevated
thermoregulatory set
point
Heat conservation, heat
production
Circulation

30. INFECTIONS MALIGNANCIES AUTOIMMUNE
CONDITIONS
OTHERS
•Hepatitis A & B
•Leptospirosis
•Malaria
•Typhoid Fever
•Leukemia
•Lymphoma
•Rheumatoid arthritis
•Rheumatic fever
•Systemic lupus
erythematosus
•Vasculitides
•Drug-induced
fever
33

31. 34
Various organ systems
which could be involved
Fever
Hematology
Nervous
Digestive
Respiratory
Urinary
Rheumatology

32. 35
Patterns of Temperature Variation
Continuous fever
• Constantly elevated above the normal level. Variability
1°C
Remittent fever
• Fluctuates daily from higher to lower levels, but is
constantly above normal
Intermittent fever
• Daily fluctuation at its lower level is below the normal
37°C

33. TYPES OF FEVER
The pattern of temperature changes may occasionally hint at
the diagnosis:
• Continuous fever: Temperature remains above normal
throughout the day and does not fluctuate more than 1 °C in
24 hours, e.g. lobar pneumonia, typhoid fever, brucellosis
• Intermittent fever: The temperature elevation is present
only for a certain period, later cycling back to normal(i.e.
Normal temp. between fever episodes), e.g. malaria, pyaemia,
or septicemia.
Following are its types
• Quotidian fever, with a periodicity of 24 hours, typical of Plasmodium
falciparum malaria
• Tertian fever (48 hour periodicity), typical of Plasmodium vivax or

34. TYPES OF FEVER
• Remittent fever: Temperature remains above normal
throughout the day and fluctuates more than 1 °C in 24
hours, e.g., infective endocarditis.
• Pel-Ebstein fever: A specific kind of fever associated
with Hodgkin's lymphoma, being high for one week and
low for the next week and so on. However, there is some
debate as to whether this pattern truly exists.

35. HISTORY TAKING IN FEBRILE
PATIENTS
• The most important step is taking a meticulous detailed
history to explore the patients problems
• Biomedical perspective- to understand the chronology
of symptoms, analyse each symptom and review each
system to localize the source of the fever.
• Contextual history- very important
• Patients perspective- to understand the patients
interpretation of the illness.
• Systems review- This is a guide not to miss anything.
Any significant finding should be moved to HPC or
PMH depending upon where you think it belongs.

36. BIOMEDICAL PERSPECTIVE
• Respiratory tract symptoms:
Sore throat, nasal discharge, sneezing-URTI
Sinus pain and headache-suggests sinusitis
cough, sputum, wheeze or breathlessness-suggests a LRTI
• Genitourinary symptoms:
Frequency of micturition, dysuria, loin pain, and vaginal or
urethral discharge-suggesting
Urinary tract infection,
Pelvic inflammatory disease and
Sexually transmitted infection (STI)

37. BIOMEDICAL PERSPECTIVE
• Abdominal symptoms: diarrhea, with or without blood, weight
loss and abdominal pain -suggesting
a) Gastroenteritis,
b) Intra-abdominal sepsis,
c) Inflammatory bowel disease,
d) Malignancy
• Skin rash: enquire about appearance and distribution as it may
provide clues to the diagnosis-
1) Macular- Measles,Rubella,toxoplasmosis
2) Haemorrhagic- Meningococcal infections, viral haemorrhagic
fever.
3) Vesicular- Chickenpox, Shingles, herpes simplex
4) Nodular- Erythema nodosum( TB and Leprosy)
5) Erythematous- Drug rashes, Dengue fever

38. BIOMEDICAL PERSPECTIVE
• Joint symptoms: joint pain, swelling or limitation of
movement is suggestive of active arthritis.
A) distribution : mono , oligo or poly arthritis
B) appearance : fleeting
1) infective arthritis- oligoarthritis
2) collagen vascular disease-fleeting
3) reactive arthritis

39. CONTEXTUAL HISTORY
Past Medical /Surgical History
Start by asking the patient if they have any medical problems
• IHD/DM/Asthma/HT/RHD, TB/Jaundice/Fits e.g. if diabetic- mention time of
diagnosis/current medication/clinic check up
Past surgical/operation history
• E.g. time/place/ what type of operation.
• Note any blood transfusion / blood grouping.
• H/O dental extractions/circumcision & any excessive bleeding during these
procedures.
Patient known to have rheumatic heart disease is at risk to develop infective
endocarditis if not given prophylaxis
• Any minor operations or procedures including endoscopies, dental interventions,
biopsies.
History of trauma/accidents
• E.g. time/place/ and what type of accident
• History of tattoo piercing

40. CONTEXTUAL HISTORY
Drug and allergy History
• dosage, timing &how long.
• Drug fever is uncommon and therefore easily missed-
The culprits include :
penicillin and
cephalosporin
sulphonamide
anti tuberculous agents
anticonvulsants particularly phenytoin
• OCT/Vitamins/Traditional /Herbal medicine &
alternative medicine such as acupuncture.
• Blood transfusion.
• Immunization against Hepatitis A &B, Typhoid fever.
• Malaria prophylaxis

41. CONTEXTUAL HISTORY
Family History
• Any familial disease/running in families e.g. breast
cancer, IHD, DM, Asthma, Arthritis
• Infections running in families as TB, Leprosy.
• Cholera, typhoid in case of epidemics.

42. CONTEXTUAL HISTORY
Personal and Social History
• Smoking history - amount, duration & type- strong risk factor for IHD
• Alcohol history - amount, duration & type-Unhealthy alcohol use is
associated with cardiomyopathy, CVA, liver cirrhosis, alcoholic hepatitis,
hepatocellular carcinoma.
• Occupation, social & education background, family social support&
financial situation, Social class.
• Home conditions-Water supply, Sanitation status in his home &
surrounding, Geographic area of living, fresh-water swimming.
• Animals / birds in his/her house- exposure to birds (psittacosis) or animals
(toxoplasmosis, brucellosis, leptospirosis)
• Consumption of unpasteurized milk or milk products (tuberculosis,
brucellosis and Q fever).
• Sexual History- Unprotected exposure to sexual partner with STI, HIV
• Illicit drug usage- injections and sharing of needles (HIV, hepatitis B &C,
infective endocarditis), site of injection (e.g Femoral vein-septic arthritis,
ilio-psoas abscess)

43. CONTEXTUAL HISTORY
TRAVEL HISTORY
Travel to an area known to be endemic for certain disease:
• Name of the area, duration of stay
• Onset of illness- (incubation period)
• 1 –10 Days- Malaria, Dengue, Salmonella
• 10 –21Days-Malaria,Typhoid,Brucella,HepatitisA
• Weeks-Months- Amoebiasis, HIV, Hepatitis
Vital questions-(Always ask about foreign travel).
a) Where have you been? …Endemic area or not ?
b) What have you done there?
c) How long were you there?
d) Did you have insect bites or contact with animals?
e) Did you take precautions/prophylaxis against malaria?
If the patient has been in an endemic area
The most common diagnoses :Malaria, Typhoid fever, Viral hepatitis,
Dengue fever
Malaria must be excluded whatever the presenting symptoms

44. SALIENT
FEATURES

 26 year old male
 Continuous Moderate to LOW grade fever
 Upper abdominal pain
 Anorexia, VOMITING
 Yellowing of sclera, color of urine, color of stool
 Fond of eating street foods
 (Temp - 38.5°C (+)
 Dry tongue, JAUNDICE
 Hepatomegaly (liver span: 13cm)

53

45. INFECTIONS
Hepatitis A/E
Hepatitis B
Malaria
Typhoid Fever
Leptospirosis
Fond of eating street foods, jaundice, vomiting, liver
jaundice, upper abdominal pain, no chills or rigors, no history of
diarrhea
No intermittent fever (2-3 days interval), no chills or rigors, no
history of blood transfusion, no travel to endemic area
Sanitary worker? No wading in flooding water, no calf
tenderness
Possible Enteric (Typhoid) Fever because of fondness of eating
street food, high grade fever, associations?
54
jaundice, no history of illicit drug use, no history of tattoo and
piercing
Liver Abscess

46. CASE 2
• A 23 year old man presented with fever with chills and rigors
for 1 week. He has cough with purulent sputum for same period,
there is also left sided chest pain which increases on coughing
and deep breathing.

47. CASE 3
• A 63 year old man presented with fever with chills and rigors
for 1 week. He has burning micturition and frequency for the
same period, there is also left sided lumbar pain.

48. CASE 4
• A 56 year old diabetic man presented with HO painful swelling
of the right knee joint along with fever for 1 week. On
examination the knee is red, hot tender, swollen and does not
flex or extend completely.

49. CASE 4
• A 5 year old child presented with HO fever for 5 days, he had
upper respiratory tract symptoms with cough and nasal
discharge. He has not been eating. His mother has noticed a
swelling bilaterally in the area of the jaw.

50. INVESTIGATIONS
• CBC: Hb, WBC, differential counts, platelet
• LFT
• Urine analysis
• Blood cultures
• Urine culture
• ESR, CRP
• Serological tests
• Peripheral smear
􀁺 ECG􀁺 CXR 􀁺 US/echo 􀁺 CT
􀁺 LP
􀁺 Arthrocentesis

51. MANAGEMENT
• General measures-
• non-pharmacological
• Anti-pyretics
• Specific management

52. • THANK YOU