What is an infection??
Definition of infection
a. Complex process of interaction between pathogen
and human body
b. Infection is composed of three factors: pathogen,
host and environment
Microbiological Classification of Infectious
Viral DNA virus
Enveloped vs non-enveloped
PATTERNS OF INFECTION IN DEVELOPED
• During the last 100 years the incidence of communicable
diseases in developed countries has fallen dramatically.
• This has been due to improved nutrition, better
sanitation and housing , immunizations and antimicrobial
• Infections such as diphtheria, poliomyelitis and tetanus
have decreased and in some locations have almost
• Smallpox, has been eradicated from the world while
another lethal infection, human immunodeficiency virus
(HIV), has emerged in pandemic proportions.
INFLUENCES ON PATTERNS OF INFECTION IN
The factors responsible for these changes are:
• Improved uptake of vaccines.
• New vaccines, e.g. conjugate vaccines for Haemophilus
influenzae type B, meningococcal type C disease,
Animal husbandry and preparation of food
• Salmonella and Campylobacter infections originating in
poultry and eggs.
• Escherichia coli type O157, causing haemorrhagic colitis
and haemolytic uraemic syndrome, associated with beef.
• Listeria infections from soft cheeses.
• Staphylococcus aureus (meticillin-resistant, MRSA; glycopeptide-resistant,
• Gram-negative bacilli (extended spectrum β-lactamase resistance,
• Streptococcus pneumoniae (penicillin),
• vancomycin-resistant enterococci (VRE) and
• multidrug-resistant Mycobacterium tuberculosis (MDRTB)
• Increase in HIV infection and other sexually transmitted diseases
• Importation of malaria
• Legionnaires' disease from holiday hotels.
• HIV infection.
• Advances in the treatment of malignant disease and in
organ transplantation, leading to infections with
Resurgence of infections
• Tuberculosis-world-wide, especially in association with
• Poliomyelitis in the Netherlands (in a religious sect
• Streptococcal infections in the USA (including rheumatic
• Measles in the USA (mainly in immigrants in inner cities)
• Diphtheria in the former Soviet Union
• Hepatitis A and typhoid fever in the former Yugoslavia
Injection drug addiction
'New' and emerging infections
1. West Nile fever in the USA
3. Avian/pandemic 'flu.
4. Swine flu
Means of Transmission of Infectious
Contact Requires direct or indirect contact (fomite, blood, or
Food or Water Ingestion of contaminated food or water
Airborne Inhalation of contaminated air
Vector-borne Dependent on biology of vector as well as infectivity
Similar to contact infection, however, the contact
may occur in utero or during delivery.
transmission by sexual intercourse.
Factors Influencing Disease Transmission
• Occupational setting
• Air quality
Host• G Age
• Nutritional status
• Antigenic stability
Barriers for Defense Against Infection:
Prevents entry of infectious organisms, unless injured.
Severe burn patients who die are usually killed by infections. So much skin is
damaged they are very vulnerable to infections.
2. Mucus membrane:
Mucous is usually rich in enzymes that will kill many pathogens
These are hair-like structures lining the respiratory tract. They work to sweep
foreign particles out of the respiratory tract.
Damaged by smoking, leaving smokers more vulnerable to infections.
Helps remove foreign material from respiratory tract.
5. Personal Hygiene
Helps reduce the number of pathogenic organisms on the skin and other
surfaces of the body.
Infection and Immunity
Manifestations of infectious process (Infection spectrum):
1) Clearance of pathogen (no infection)
2) Covert infection (subclinical infection)
3) Overt infection (Clinical infection or apparent infection)
4) Carrier states
Health carrier after covert infection.
Convalescent carrier after overt infection.
Incubatory carrier before onset of disease.
According to carrier time : #acute (transient) carrier
5) Latent infection.
Infection has many effects on the body, They may be
CLINICAL EFFECTS OF INFECTION ON THE BODY -
• Fever; anorexia, protein catabolism, acute-phase protein
response, hypoalbuminaemia, low serum iron,
sequestration of iron, anaemia, neutrophilia
• Inflammation; pain, dysfunction, tissue damage
• Convulsions; especially in children
• Confusion; especially in the elderly
• Haemorrhage; haemolytic anaemia, intravascular
• Organ failure.
CLINICAL EFFECTS OF INFECTION ON THE BODY-Chronic
• Weight loss and muscle-wasting
• Malnutrition; especially associated with diarrhoea
• Retardation of growth and intellect in children
• Anaemia; iron sequestration, maturation arrest in
marrow, folate deficiency
• Tissue destruction; e.g. lung in pneumonia or
tuberculosis, nerves in leprosy, liver in hepatitis B
• Post-infective syndromes; e.g. lactose intolerance,
malabsorption, irritable colon, depression, post-viral
CLINICAL EFFECTS OF INFECTION ON THE BODY-Allergic
• Rash; e.g. urticaria with helminths, maculo-papular in
typhoid and endocarditis, erythema nodosum in
• Arthritis; e.g. in rheumatic fever, Reiter's syndrome
• Pericarditis; e.g. in meningococcal infection
• Encephalitis; e.g. in measles or following vaccines
• Peripheral neuropathy; e.g. in post-infective polyneuritis
• Haemolytic anaemia; e.g. in infectious mononucleosis
• Nephritis; e.g. in streptococcal infection
Clinical effect of infection on the body-toxic
or toxin mediated
• Erythematous rash in streptococcal infection
• Multisystem disturbance in staphylococcal or
streptococcal toxic shock syndrome
• Diarrhea; e.g. staphylococcal enterotoxin, Bacillus
• Organ disturbance; e.g. diphtheria
• Neurological; e.g. tetanus, botulinum, diphtheria
• The incubation period
is the period between the invasion of the tissues by
pathogens and the appearance of clinical features of
• The period of infectivity
is the time that the patient is infectious to others.
INCUBATION PERIODS OF IMPORTANT INFECTIONS
Short incubation periods (< 7 days):
• Bacillary dysentery 1-7 days
• Cholera Hours-5 days ( 2-3 hours)
• Diphtheria 2-5 days
• Gonorrhoea 2-5 days
• Scarlet fever 1-3 days
Intermediate incubation periods (7-21 days)
• Chickenpox 14-21 days
• Measles 7-14 days
• Mumps 12-21 days
• Poliomyelitis 3-21 days
• Rubella 14-21 days
Long incubation periods (> 21 days)
• Brucellosis Days-months
• Hepatitis B 6 weeks-6 months
• Rabies Variable
• Tuberculosis Months-years
PERIODS OF INFECTIVITY IN CHILDHOOD
Disease Infectious period
• Chickenpox 5 days before rash to 6 days after last
• Measles From onset of prodromal symptoms to 4
days after onset of rash
• Mumps 3 days before salivary swelling to 7 days
• Rubella 7 days before onset of rash to 4 days after
Prevention of infection
Any reduction in the reservoirs of infection will naturally reduce the
incidence of disease produced by these organisms.
Endogenous reservoirs may be reduced by
• physical isolation of cases whilst infective
• physical separation of animal sources from human hosts and
• their rapid treatment will reduce zoonoses.
Blockage of transmission by
careful infection control will also halt the spread of infection.
Public health measures control spread of infection and
• vaccination may improve 'herd immunity' in communities.
• Prophylactic immunoglobulin may help some individuals at high risk
INDICATIONS FOR CHEMOPROPHYLAXIS IN
CONTACTS OF PATIENTS WITH INFECTIOUS DISEASE
Infection Antimicrobiol agent Adult dose
• Diphtheria Erythromycin 500 mg 6-hourly for 5 days
• Meningococcal Rifampicin 600 mg 12 hrly 2 days or
Ciprofloxacin 500 mg single dose
• Whooping cough Erythromycin 500 mg 6-hourly for 7 days
• Tuberculosis Isoniazid 300 mg daily for 6 months
INDICATIONS FOR PROPHYLACTIC
Human specific immunoglobulin
• Virus B hepatitis (needle stick injuries, sexual partner)
• Tetanus (susceptible injured patients)
• Rabies (post-exposure protection)
• Chickenpox (immunosuppressed children, adults and
• Respiratory syncytial virus infection (high-risk infants,
e.g. premature-investigational use)
CHARACTERISTICS OF EFFECTIVE VACCINES
• Long-lasting effects
• Cost Inexpensive to produce and deliver
• Administration Easy to deliver with no side-effects
GUIDELINES FOR IMMUNISATION AGAINST
• The principal contraindication to inactivated vaccines is a significant reaction
to a previous dose
• Live vaccines should not be given to pregnant women or to the
immunosuppressed, or in the presence of an acute infection
• If two live vaccines are required, they should be given either simultaneously
in opposite arms or 3 weeks apart
• Live vaccines should not be given for 3 months after an injection of human
normal immunoglobulin (HNI)
• HNI should not be given for 2 weeks after a live vaccine
• Hay fever, asthma, eczema, sickle-cell disease, topical corticosteroid
therapy, antibiotic therapy, prematurity and chronic heart and lung diseases,
including tuberculosis, are not contraindications to immunisation
IMMUNISATION SCHEDULE FOR INFANTS RECOMMENDED BY
THE WHO EXPANDED PROGRAMME ON IMMUNISATION
Vaccine Birth 6 weeks 10 weeks 14 weeks 9months
Oral polio * * * *
Diphtheria, * * *
Hepatitis B * * *