Tuberculosis Case Study

Presenter

Xoliswa Poswa

TB Laboratory, NHLS/CMID

Case History

• 47 year old man• Presents to the clinic with a 4

weeks history of cough• He noticed a tinge of blood in

his sputum• He has lost weight and is also

sweating a lot at night • The nurse suspected

tuberculosis and asked him to spit into a specimen bottle

• A diagnosis of TB is confirmed by the laboratory using smear microscopy

Microbiological Characteristics• Microscopic examination of a

smear of sputum stained by Ziehl-Neelsen’s method or by auramine shows– acid fast bacilli– may be straight or slightly

curved• Acid fast – unique

characteristic of mycobacteria cell wall due to cell wall constituents– lipid content is very high– hydrophobic– impermeable to basic aneline

bacteriological stains– major determinant of virulance

Microbiological Characteristics

• Lipid fraction of M. tuberculosis cell wall has 3 major components

• Mycolic acid, a unique lipid found in cell wall of MTB

– strong hydrophobic molecules forming lipid shell around the cell thus affecting permeability

– significant determinant of virulance for MTB i.e prevent attack of mycobacteria by components of immune system (cationic proteins, lysozymes and oxygen radicals in the phagocytic granules

Microbiological Characteristics

• Cord factor – responsible for serpentine

cording

– it is toxic to human cells, prevents migration of certain immune cells i.e polymorphonuclear cells

– produced abundantly in virulent strains

• Wax-D – cell wall envelope

Microbiological Characteristics

• In summary the high concentration of lipids is associated with the following properties of bacterium:– Impermeability to stains and dyes– Resistance to many antibiotics– Resistance to killing by acidic or alkaline compounds– Resistance to osmotic lysis by complement

component of immune system– Resistance to lethal oxidation and survival within

macrophages

Case cont:

• The patient was questioned further:– He shared accommodation with his late

nephew who had been coughing for the past few months

– He now looks after his nephew’s 4 year old daughter who came to stay with them 2 weeks ago

Pathogenesis of disease

Pathogenesis of disease

• Condition for developing infection:• Exposure

– Frequency– Duration– Concentration of bacilli– Virulence

• Host immunity– Extremes of age i.e very young/old– Malnutrition– Alcoholism– HIV/AIDS– Drugs that depress immunity e.g corticosteroids

Management

• Diagnosis – Microscopy of sputum smear– Cultivation of sputum (for growth of mycobacteria)

• Drug treatment– The patient was given treatment, a combination of 4

drugs which he had to take under supervision for 6 months

– Rationale for combination therapy:• The various drugs target different forms of bacilli i.e. rapidly

growing and dormant forms• Prevent development of resistance• Prevent development of relapse of disease due to dormant

bacilli

Management

• Prevention:– he was told to bring the child to clinic to screen for

tuberculosis– screening included intradermal injection with a

mixture of proteins derived from MTB (skin test)• Induration at injection site occurs within 48-72 hours in a

sensitized person (exposed to MTB)

– his wife was also educated on the signs and symptoms of TB and to report to clinic should she develop any one of them

Management

– the skin test was negative and the child was otherwise well with no signs suggestive of active disease/she had BCG vaccination at birth

– nurse elected to give prophylactic treatment with one anti-TB drug for 6 months

Management

– Rationale for screening: • Children under 5 years of age who are exposed to

MTB are more likely to progress to disease following infection

– Rationale for prophylaxis:• prevent development of disease after exposure in

a young child at risk• single drug can be used as there are potentially

very few bacilli in the absence of active disease and development of resistance unlikely

Management

• Summary:• Treatment

– 4 drug combination for 6 months under supervision

• Immune prophylaxis– vaccination with BCG (bacille Calmette-Guerin)

vaccine at birth– this does not prevent infection but allows body to

react quickly to limit replication of mycobacteria

• Chemoprophylaxis – with a single anti-TB drug (isoniazid)