1. INFECTIONSINFECTIONS

2. Important Definitions:Important Definitions:
Infection:Infection:
““A pathological process/disease occurring due to a micro-organism or aA pathological process/disease occurring due to a micro-organism or a
microbial product.”microbial product.”
Host:Host:
““A living organism that harbors or nourishes another organism.”A living organism that harbors or nourishes another organism.”
e.g., man is a host of E. histolytica (the cause of Amebiasis).e.g., man is a host of E. histolytica (the cause of Amebiasis).
Carrier:Carrier:
““A person who harbours the micro-organism of a disease andA person who harbours the micro-organism of a disease and excrete themexcrete them
(e.g., in feces & urine) without himself suffering from the symptoms.” e.g.;(e.g., in feces & urine) without himself suffering from the symptoms.” e.g.;
1. Nasal carriers: Corynebacterium diphtherae & Streptococcus1. Nasal carriers: Corynebacterium diphtherae & Streptococcus
2. Throat carriers: Diphtheria, Neisseria meningitidis2. Throat carriers: Diphtheria, Neisseria meningitidis
3. Faecal carriers: Vibrio cholrae, Salmonella typhi.3. Faecal carriers: Vibrio cholrae, Salmonella typhi.
4. Urinary carriers: Neisseria gonorrhae, Typhoid.4. Urinary carriers: Neisseria gonorrhae, Typhoid.
Incubation period:Incubation period:
““The time interval which elapses between the entrance of the pathogen intoThe time interval which elapses between the entrance of the pathogen into
the body and to the appearance of first symptom of the disease”. e.g.the body and to the appearance of first symptom of the disease”. e.g.
Typhoid 7-21 days, Hepatitis-A 2-6 wks.Typhoid 7-21 days, Hepatitis-A 2-6 wks.

3. Important Definitions:Important Definitions:
Contagious:Contagious:
““An infection which is capable of being transmitted from one person toAn infection which is capable of being transmitted from one person to
another” e.g. STDs.another” e.g. STDs.
Opportunistic infection:Opportunistic infection:
““Infection by organism that normally do not produce disease but take theInfection by organism that normally do not produce disease but take the
opportunity provided by a defect in the host’s defense to infect the host andopportunity provided by a defect in the host’s defense to infect the host and
cause disease.” e.g., infection by Pneumocystis carinii in AIDS patients.cause disease.” e.g., infection by Pneumocystis carinii in AIDS patients.
Epidemic:Epidemic:
““The unusual occurrence of a disease in excess of the expected occurrenceThe unusual occurrence of a disease in excess of the expected occurrence
in a community or region is called Epidemic” e.g., hepatitis-A.in a community or region is called Epidemic” e.g., hepatitis-A.
Sterilization:Sterilization:
““A process which leads to the destruction of all micro-organisms includingA process which leads to the destruction of all micro-organisms including
their spore forms.”their spore forms.”
Disinfection:Disinfection:
The process of destruction of vegetative (non spore forming stage) forms ofThe process of destruction of vegetative (non spore forming stage) forms of
the microorganisms only and not the spores.”the microorganisms only and not the spores.”

4. Routes/Mode of TransmissionRoutes/Mode of Transmission
1) Inhalation1) Inhalation::
a) Directa) Direct:: Herpes Simplex, Infection mononucleosis, Hepatitis-B.Herpes Simplex, Infection mononucleosis, Hepatitis-B.
b) Dropletb) Droplet: M. tuberculosis, diphtheria.: M. tuberculosis, diphtheria.
c) Dustc) Dust: Staphylococci.: Staphylococci.
2)2) IngestionIngestion::
a) Direct Contacta) Direct Contact: Faeces, hands.: Faeces, hands.
b) Food borneb) Food borne: Food handling.: Food handling.
c) Water borne:c) Water borne: Hepatitis, typhoid.Hepatitis, typhoid.
3)3) Inoculation:Inoculation:
a) Simple contacta) Simple contact
b) Wound infectionb) Wound infection
c) Injections:c) Injections:
Medical injectionsMedical injections
Insect bites.Insect bites.
4)4) Transplacental (through placentaTransplacental (through placenta):):
AIDS, Hepatitis-B.AIDS, Hepatitis-B.

5. Types of Infections:Types of Infections:
Infections could be of following types:Infections could be of following types:
BacterialBacterial
ViralViral
ParasiticParasitic
FungalFungal

6. Bacterial InfectionsBacterial Infections
Bacterial infections could involve any part of body and thereforeBacterial infections could involve any part of body and therefore
are grouped as follows:are grouped as follows:
Skin & Soft Tissues Infections.Skin & Soft Tissues Infections.
GIT Infections.GIT Infections.
Respiratory Tract Infections (RTIs).Respiratory Tract Infections (RTIs).
Urinary Tract Infections (UTIs)Urinary Tract Infections (UTIs)
Pelvic Inflammatory Diseases (PIDs)Pelvic Inflammatory Diseases (PIDs)
Sexually Transmitted Diseases (STDs)Sexually Transmitted Diseases (STDs)
Intra-abdominal infections e.g. peritonitisIntra-abdominal infections e.g. peritonitis
Infections of the CNS e.g. meningitisInfections of the CNS e.g. meningitis
Infections of Bones & Joints e.g. osteomyelitisInfections of Bones & Joints e.g. osteomyelitis
Anaerobic Bacterial Infections e.g. tetanusAnaerobic Bacterial Infections e.g. tetanus
In addition bacterial infections could involve any other organ e.g.In addition bacterial infections could involve any other organ e.g.
ocular (eye) infections, cardiac infections e.g. Endocarditis, etc.ocular (eye) infections, cardiac infections e.g. Endocarditis, etc.

8. Skin, Soft Tissue InfectionsSkin, Soft Tissue Infections
Cellulitis:Cellulitis:
A diffuse, spreading, acute inflammation characterized by swellingA diffuse, spreading, acute inflammation characterized by swelling
and hyperemia, usually caused by Streptococcus pyogenes.and hyperemia, usually caused by Streptococcus pyogenes.
Folliculitis:Folliculitis:
A superficial or deep bacterial infection of the hair follicle. It is usuallyA superficial or deep bacterial infection of the hair follicle. It is usually
caused by S. aureus.caused by S. aureus.
Furuncles (Boils):Furuncles (Boils):
Acute, tender, perifollicular inflammation caused by Staphylococci.Acute, tender, perifollicular inflammation caused by Staphylococci.
Carbuncle:Carbuncle:
A cluster of furuncles with spread of infection subcutaneously.A cluster of furuncles with spread of infection subcutaneously.
Impetigo:Impetigo:
A superficial vesicopustular skin infection. It is usually caused by S.A superficial vesicopustular skin infection. It is usually caused by S.
aureus.aureus.

11. G.I.T InfectionsG.I.T Infections
Infections that involve any organ of the gastrointestinal tract are called GITInfections that involve any organ of the gastrointestinal tract are called GIT
infections.These are usually caused by gram negative enterococci.infections.These are usually caused by gram negative enterococci.
Typhoid Fever (Enteric Fever):Typhoid Fever (Enteric Fever):
Typhoid is a communicable disease caused byTyphoid is a communicable disease caused by Salmonella typhi.Salmonella typhi.
Especially prevalent in undeveloped countries, this disease is transmittedEspecially prevalent in undeveloped countries, this disease is transmitted
through feces or urine discharged by an infected person or a carrier. Thisthrough feces or urine discharged by an infected person or a carrier. This
may contaminate a water supply (because of inadequate public sanitation) ormay contaminate a water supply (because of inadequate public sanitation) or
infect the food through the hands of the carrier (due to poor personalinfect the food through the hands of the carrier (due to poor personal
hygiene).hygiene).
The bacteria enter the body via gastrointestinal tract and gain access to theThe bacteria enter the body via gastrointestinal tract and gain access to the
blood stream through lymphatic channels.blood stream through lymphatic channels.
Symptoms:Symptoms:
StepladderStepladder fever, intestinal inflammation, lassitude, swollen lymph glandsfever, intestinal inflammation, lassitude, swollen lymph glands
and spleen and a rose-colored rash.and spleen and a rose-colored rash.
The mortality rate is 10% in untreated cases.The mortality rate is 10% in untreated cases.
Other GIT infections include, bacillary dysentery, cholera, etc.Other GIT infections include, bacillary dysentery, cholera, etc.

12. Respiratory Tract InfectionsRespiratory Tract Infections
The infections that involve the respiratory organs are called RTIs.The infections that involve the respiratory organs are called RTIs.
These are most commonly caused by gram-positive cocci. These are broadly divided into two main types:These are most commonly caused by gram-positive cocci. These are broadly divided into two main types:
1. Upper RTIs1. Upper RTIs
2. Lower RTIs2. Lower RTIs
1. UPPER RTIs:1. UPPER RTIs:
More common in childhood and early adult life:More common in childhood and early adult life:
A)A) Ear & Mastoid:Ear & Mastoid:
Acute otitis mediaAcute otitis media
Chronic suppurative otitis mediaChronic suppurative otitis media
Malignant otitis mediaMalignant otitis media
Acute mastoiditisAcute mastoiditis
Chronic mastoiditisChronic mastoiditis
B)B) Sinusitis:Sinusitis:
AcuteAcute
ChronicChronic
C)C) Pharynx:Pharynx:
PharyngitisPharyngitis
Tonsillar or peritonsillar abscessTonsillar or peritonsillar abscess
Membranous pharyngitisMembranous pharyngitis
EpiglottitisEpiglottitis
LaryngitisLaryngitis
2. LOWER RTIs:2. LOWER RTIs:
Bronchitis/bronchiolitisBronchitis/bronchiolitis
PneumoniaPneumonia
Lung abscess/empyemaLung abscess/empyema
5. Bronchiectasis.5. Bronchiectasis. Irreversible, focal, bronchial dilatation usually accompanied by infection.Irreversible, focal, bronchial dilatation usually accompanied by infection.

13. PneumoniaPneumonia
““It is the inflammation of the lung parenchyma”.It is the inflammation of the lung parenchyma”.
Classification:Classification:
Primary::Primary:: Those which are caused by specific organisms.Those which are caused by specific organisms.
Secondary/Aspiration Pneumonia:Secondary/Aspiration Pneumonia:
Etiology:Etiology:
Most Common:Most Common:
Streptococcus pneumoniae (Pneumococcus).Streptococcus pneumoniae (Pneumococcus).
Common:Common:
Staphylococcus aureusStaphylococcus aureus
Legionella pneumophilaLegionella pneumophila
Mycoplasma pneumoniaeMycoplasma pneumoniae
Moraxalla (Branhamella) catarrhalisMoraxalla (Branhamella) catarrhalis
Uncommon:Uncommon:
H. influenzaeH. influenzae
K. pneumoniaeK. pneumoniae
Strep. pyogenesStrep. pyogenes
Pseudomonas aeruginosaPseudomonas aeruginosa
Signs and Symptoms:Signs and Symptoms:
Usually there is sudden onset of fever with rigors, loss of appetite, headache and aching pains in the bodyUsually there is sudden onset of fever with rigors, loss of appetite, headache and aching pains in the body
and limbs, alongwith localized chest pain and productive cough.and limbs, alongwith localized chest pain and productive cough.
Pneumonia could be fatal especially in children if not treated in time.Pneumonia could be fatal especially in children if not treated in time.
Complications:Complications:
Sepsis: ARDS, septic shockSepsis: ARDS, septic shock
Empyema, pericarditis, endocarditis, septic arthritis.Empyema, pericarditis, endocarditis, septic arthritis.

14. Urinary Tract InfectionsUrinary Tract Infections
The infections that involve the urinaryThe infections that involve the urinary
tract organs are called UTIs e.g.tract organs are called UTIs e.g.
KidneyKidney PyelonephritisPyelonephritis
Urinary BladderUrinary Bladder CystitisCystitis
UrethraUrethra UrethritisUrethritis
ProstateProstate ProstatitisProstatitis

15. Urinary Tract InfectionsUrinary Tract Infections
ACUTE UTIsACUTE UTIs
Etiology and Pathogenesis:Etiology and Pathogenesis:
Usually there is ascending infection from perineum to vagina to urethra and finallyUsually there is ascending infection from perineum to vagina to urethra and finally
to bladder due to presence of vesico-ureteric reflux (VUR).to bladder due to presence of vesico-ureteric reflux (VUR).
Strictures, calculus (stones), tumors, prostatic hypertrophy predisposes to infection.Strictures, calculus (stones), tumors, prostatic hypertrophy predisposes to infection.
Instrumentation and catheterization also increases the risk.Instrumentation and catheterization also increases the risk.
Common pathogens are E.coli (75%), Klebsiella sp., Proteus mirabilis, EnterobacterCommon pathogens are E.coli (75%), Klebsiella sp., Proteus mirabilis, Enterobacter
sp (10-15%), Staphylococci and Streptococcus faecalis (2-3%).sp (10-15%), Staphylococci and Streptococcus faecalis (2-3%).
Signs and Symptoms:Signs and Symptoms:
Rapid onset of pain in flanks, fever with chills, and vomiting.Rapid onset of pain in flanks, fever with chills, and vomiting.
There may be frequency (frequent urination) and dysuria (pain during urination).There may be frequency (frequent urination) and dysuria (pain during urination).
Abdominal rigidity and tenderness.Abdominal rigidity and tenderness.
CHRONIC UTIs:CHRONIC UTIs:
These are caused by recurrent UTIs and VUR. Congenital abnormalities of urinaryThese are caused by recurrent UTIs and VUR. Congenital abnormalities of urinary
tract predispose to infection.tract predispose to infection.
Fever and abdominal pain are not very common in chronic UTIs.Fever and abdominal pain are not very common in chronic UTIs.
Complications:Complications:
Pyonephrosis.Pyonephrosis.
Renal failureRenal failure

16. Pelvic Inflammatory DiseasesPelvic Inflammatory Diseases
This group includes the infections of the female pelvic organsThis group includes the infections of the female pelvic organs
CervixCervix CervicitisCervicitis
UterusUterus EndometritisEndometritis
Fallopian TubesFallopian Tubes SalpingitisSalpingitis
OvariesOvaries OophritisOophritis
Etiology and Pathogenesis:Etiology and Pathogenesis:
Commonly occur in women under 35 yrs of age who are sexually active.Commonly occur in women under 35 yrs of age who are sexually active.
Microorganisms are transmitted by intercourse, childbirth, abortion, IUCDs, causingMicroorganisms are transmitted by intercourse, childbirth, abortion, IUCDs, causing
ascending type of infection.ascending type of infection.
Common organisms are; Chlamydia trachomatis (40-50%), Neisseria gonorrhoae,Common organisms are; Chlamydia trachomatis (40-50%), Neisseria gonorrhoae,
Staphylococci and StreptococciStaphylococci and Streptococci
Signs and Symptoms:Signs and Symptoms:
Acute:Acute:
Main symptoms are lower abdominal pain and tenderness, high fever, vomiting andMain symptoms are lower abdominal pain and tenderness, high fever, vomiting and
purulent cervical discharge.purulent cervical discharge.
Chronic:Chronic:
These include chronic pain and menstrual irregularities.These include chronic pain and menstrual irregularities.
Complications:Complications:
Pelvic scarring, adhesion formation and later infertility.Pelvic scarring, adhesion formation and later infertility.
Abscesses may form anywhere in the genital tract.Abscesses may form anywhere in the genital tract.
Pyosalpinx, hydrosalpinx.Pyosalpinx, hydrosalpinx.

17. Sexually Transmitted DiseaseSexually Transmitted Disease
This group includes all those infections, which are transmittedThis group includes all those infections, which are transmitted via the sexualvia the sexual
route. These infections involve the genitourinary organs e.g. cervix, urethra,route. These infections involve the genitourinary organs e.g. cervix, urethra,
therefore PIDs, UTIs and STDs are often studied together. These can occurtherefore PIDs, UTIs and STDs are often studied together. These can occur
both in males and females.both in males and females.
GONORRHOEA:GONORRHOEA:
It is a common STD caused by N. gonorrhae (Gonococcus).It is a common STD caused by N. gonorrhae (Gonococcus).
Gonorrhoea usually presents as acute urethritis (inflammation of the urethra)Gonorrhoea usually presents as acute urethritis (inflammation of the urethra)
both in males & females. Later on it may spread to involve the surroundingboth in males & females. Later on it may spread to involve the surrounding
organs e.g., prostate, seminal vesicles in males and cervix, uterus, fallopianorgans e.g., prostate, seminal vesicles in males and cervix, uterus, fallopian
tubes and ovaries in females.tubes and ovaries in females.
Pharynx is occasionally involved in both males and females and is calledPharynx is occasionally involved in both males and females and is called
Gonococcal Pharyngitis. It probably results through oral transmission orGonococcal Pharyngitis. It probably results through oral transmission or
blood stream. This is not very common.blood stream. This is not very common.
Course of the Disease:Course of the Disease:
Usually the disease resolves spontaneously but sometimes it progresses andUsually the disease resolves spontaneously but sometimes it progresses and
if not treated in time it may lead to complications e.g., arthritis, endocarditisif not treated in time it may lead to complications e.g., arthritis, endocarditis
or the involvement of the surrounding tissues.or the involvement of the surrounding tissues.