BACTERIAL INFECTIONS OF R.T. - PowerPoint Presentation

Slide1

BACTERIAL

INFECTIONS OF R.T.

TUBERCULOSIS

Tuberculosis

remains one of the major health

problems in

many tropical countries

; in some

countries the

situation is being aggravated by dense

overcrowding

in

urban slums. An estimated 8–10

million people

develop overt tuberculosis annually

as a

result of primary infection, endogenous

reactivation or

exogenous reinfection.

The worst

affected country

is India which is estimated to have 30%

of the

world’s cases of TB and 37% of the deaths

from

TB.

The

coexistence of HIV infection and

tuberculosis

has

been hailed as one

of the most

serious threats

to human health

since the Black Death

and has

been labelled ‘the cursed duet

’.

Drug-resistant tuberculosis is on the increase

in many

countries of the world

.

Tuberculosis presents a wide variety of

clinical forms

, but pulmonary involvement is

common and

is most important epidemiologically as it

is primarily

responsible for the transmission of

the infection.

The

causative agent is

Mycobacterium

tuberculosis

, the

tubercle bacillus. The

human

type produces

most

of the

pulmonary lesions, also some

extrapulmonary

lesions

; the

bovine strain

of the

organism mainly

accounts for

extrapulmonary

lesions

. Other

types of

M. tuberculosis

(

avian and

atypical strains

)

rarely cause disease in humans

, but

infection may

produce immunological changes, with

a non-specific

tuberculin skin

reaction.

Tubercle

bacilli

survive for long periods in

dried sputum

and dust

.

Epidemiology

Tuberculosis has a

worldwide distribution

.

Until recently

, it was

absent from a few isolated

communities

where

the local populations are now

showing widespread

infections with severe

manifestations on

first contact with tuberculosis.

RESERVOIR

Humans

are the

reservoir of the human strain

and

patients

with pulmonary infection

constitute

the

main

source of infection.

The

reservoir of the bovine strain is cattle

,

with

infected

milk and meat

being

the main sources

of infection

.

TRANSMISSION

Transmission

of infection is mainly

air-borne

by droplets

,

droplet nuclei and dust

; thus it is

enhanced by

overcrowding in poorly ventilated

accommodation

. Infection

may also occur by

ingestion, especially

of contaminated milk and infected

meat

HOST

FACTORS

The host response is an important factor in

the epidemiology

of tuberculosis. A primary

infection may

heal, the host acquiring immunity in

the process

. In some cases the primary lesion

progresses to

produce extensive disease locally, or

infection may

disseminate to produce metastatic or

military lesions

. Lesions that are apparently healed may

subsequently break

down with reactivation of

disease. Certain

factors such as malnutrition, measles

infection and

HIV infection, use of

corticosteroids and other

debilitating conditions predispose to

progression and

reactivation of the disease.

Control

In planning a

programme

for the control of

tuberculosis, the

entire

population

can be

conveniently considered

as falling into

four groups

:

■

No previous exposure

to tubercle bacilli

–

they would

require protection from infection

.

■

Healed primary infection

– they have

some

immunity

but

must be

protected

from reactivation

of disease

and reinfection.

■

Diagnosed active disease

– they must have

effective

treatment

and remain

under supervision

until they

have recovered fully.

■

Undiagnosed active disease

– without treatment

the disease

may progress with further

irreversible damage

. As potential sources of infection,

they constitute

a danger to the

community.

The

control of tuberculosis can be

considered

at the

following levels of prevention:

■ general health promotion;

■ specific protection – active

immunization, chemoprophylaxis

, control of animal reservoir;

■ early diagnosis and treatment;

■ limitation of disability;

■ rehabilitation;

■ surveillance.

GENERAL HEALTH PROMOTION

Improvement in housing (good ventilation, avoidance of overcrowding) will reduce the chances of air-borne infections. Health education should be directed at producing better personal habits with regard to spitting and coughing. Good nutrition enhances host immunity.

SPECIFIC PROTECTION

Three measures are available: (

i

)active immunization with BCG (

Bacille

Calmette

Guerin);(ii)chemoprophylaxis; and (iii) control of animal tuberculosis.

BCG vaccination

This vaccine contains

live attenuated tubercle bacilli of the bovine strain

. It may be administered

intradermally

by syringe and needle or by the

multiple-puncture technique

. It confers significant but not absolute immunity; in particular, it protects against the disseminated

miliary

lesions of tuberculosis and tuberculous meningitis.

Disadvantages

Various complications have been encountered

in the

use of BCG. These may be:

■

local

– chronic ulceration

, discharge, abscess

formation and

keloids;

■

regional

– adenitis

which may or may not

suppurate or

form sinuses

;

■

disseminated

– a rare complication.

The protective efficacy of BCG vaccine has

varied considerably

in different countries.

Chemoprophylaxis

Isoniazid

has proved an effective

prophylactic agent

in preventing infection and progression

of infection

to severe

disease. Treatment

with isoniazid

for 1 year is

recommended for

the following groups:

■ close contacts of patients;

■ persons who have converted from

tuberculin negative to

tuberculin-positive in the

previous year;

■

children under 3 years who are

tuberculin positive from

naturally acquired

infection.

The

tuberculin-negative person

may be

protected by

BCG or isoniazid

, the decision as

to which

method to use would depend on local

factors, the

acceptability of regular drug therapy,

and the

availability of effective supervision

.

SURVEILLANCE OF TUBERCULOSIS

For effective control of tuberculosis

, there should be a surveillance system to collect, evaluate and

analyse

all pertinent data, and use such knowledge to plan and evaluate the control programme.

The sources of data will include:

■ notification of cases;

■ investigation of contacts, post-mortem reports; ■ special surveys – tuberculin, sputum, chest X-ray; ■ laboratory reports on isolation of organisms including the pattern of drug sensitivity; ■ records of BCG immunization – routine and mass programmes; ■ housing, especially data about overcrowding; ■ data about tuberculosis in cattle; ■ utilization of anti tuberculous drugs.

Key operations of a national

TB programme

(NTP)

All countries where TB is a public health

problem should

establish

a national TB programme, the

key specifics

of which are:

■ establishment of a central unit to guarantee

the political

and operational support for the

various levels

of the programme;

■ prepare a programme manual;

■ establish a seconding and reporting system;

■ initiate a training programme;

■ establish microscopy services

;

■

establish treatment services;

■ secure a regular supply of drugs and

diagnostic material

;

■ design a plan of supervision;

■ prepare a project development

plan.

The

overall objective is to reduce mortality,

morbidity and

transmission of TB until it is no longer

a threat

to public health as speedily as possible

.

PNEUMONIAS

A variety of organisms may cause acute infection of the lungs.

The non-

tuberculous

pneumonias are usually classified into three groups:

■ pneumococcal; ■ other bacterial; ■ atypical.

Pneumococcal pneumonia

Pneumococcal infection of the lungs

characteristically produces

lobar consolidation but

bronchopneumonia

may

occur in susceptible groups.

Typically, the

untreated case resolves by crisis, but

with

antibiotic treatment

there is usually a rapid

response

.

Metastatic

lesions

may occur in the meninges,

brain, heart

valves, pericardium or joints. Pneumonia

and bronchopneumonia

are two of the major causes

of death

in the tropics, especially in children.

The

incubation period is 1–3 days

.

EPIDEMIOLOGY

The

disease has a worldwide distribution

.

Reservoir

Humans

are the

reservoir

of infection;

this includes

sick patients as well as carriers.

Transmission

Transmission

is by

air-borne infection

and

droplets

,

by

direct contact

or through contaminated

articles. Pneumococcus

may persist in the dust for some time.

Host factors

All ages are susceptible

, but the clinical

manifestations are

most severe at the extremes of age.

Pneumonia

may complicate viral infection

of the

respiratory tract

. Exposure, fatigue,

alcohol and

pregnancy apparently lower resistance to

this infection

. On recovery, there is some immunity

to the

homologous type

.

CONTROL

S. pneumoniae

generally responds well to

penicillin but

strains with intermediate resistance occur

and strains

with high resistance have been isolated

The

general measures for the

prevention

of

respiratory infections

apply –

avoidance of

overcrowding

,

good

ventilation

and improved

personal hygiene

with regard to coughing and

spitting.

Prompt

treatment of cases with antibiotics

penicillin,

cephalosporins

,

vancomycin

would

prevent complications

.

Chemoprophylaxis with

penicillin is

indicated in cases of outbreaks in institutions

.

A polyvalent

polysaccharide vaccine is available

and has

been successfully used in children with

sickle cell

disease.

It is not effective in children under

2years

.

OTHER BACTERIAL PNEUMONIAS

The

other bacteria which can cause

pneumonia include

:

Staphylococcus

aureus

, Chlamydia

pneumoniae,

Haemophilus

influenzae

, Legionella

pneumophila

, Mycoplasma

pneumoniae

and

Chlamydia

psittaci

. Although

in some cases

one particular

organism

predominates

, it is not unusual to

encounter

mixed

infections

, especially

in persons

with chronic

lung disorders

. The organisms can be

isolated

on

culture of the sputum or

occasionally from

blood.

EPIDEMIOLOGY:

These

infections have a

worldwide

distribution

and

the organisms are commonly found

in humans

and their environment.

Transmission

is

by droplets

,

air-borne

infection and

contact

.

Host factors:

The occurrence of infection is largely determine by host factors such as the presence of viral

infection of the respiratory tract (e.g. influenza, measles) or debilitating illness (e.g. diabetes, chronic renal failure). Patients suffering from chronic bronchitis are particularly susceptible.

CONTROL:

The

frequency of these bacterial pneumonias can be diminished by:

1

The prevention or prompt treatment of respiratory disease:

■ viral infection (e.g. measles and influenza vaccination);

■ upper respiratory infection (especially in children and the elderly);

■ chronic lung disease (especially chronic bronchitis).

2

Improvement in housing conditions.

Mycoplasma pneumonia

This

is an

acute febrile illness

usually

starting

with signs

of an upper respiratory infection

,

later

spreading to

the bronchi and

lungs

. Radiological

examination of the lungs

shows hazy

patchy

infiltration.

The

incubation period

is usually about

12

days

, ranging

from 7 to 21 days.

The

infective agent

is

Mycoplasma

pneumoniae

(

pleuro

-pneumonia-like organism

).

EPIDEMIOLOGY

The

geographical distribution is

worldwide

.

Humans

are the

reservoir of infection

.

It

is

transmitted from

sick patients as well as from persons

with subclinical

infection.

Transmission is by

droplet

infection

and by

contact

.

Only

a small proportion

of infected

persons (1 in 30) show signs of illness

.

After recovery

, the patient is immune for an

undefined period

.

M. pneumoniae

spreads easily in

institutions such

as schools, and military units, the highest

incidence is

in under 20-year-olds

.

CONTROL

General measures for the control of

respiratory diseases apply.

Treatment

with

tetracycline is

advocated in cases of pneumonia.

MENINGOCOCCAL INFECTION

A

variety of clinical manifestations may be

produced when

human beings are infected

with

Neisseria

meningitidis

: the typical clinical picture

is of

acute pyogenic meningitis with fever,

headache, nausea

and vomiting, neck stiffness, loss of

consciousness and

a characteristic petechial rash

is often

present. The wide spectrum of clinical

manifestations ranges

from fulminating disease

with shock

and circulatory collapse to relatively

mild

meningococcaemia

without meningitis

presenting as

a febrile illness with a rash.

The carrier state

is common. The

incubation period is usually 3–4 days,

but may

be 2–10 days

.

Epidemiology

There is a

worldwide distribution of this infection

. Sporadic cases and epidemics occur in most parts of the world, in particular South America and the Middle East, but also in the developed countries of the temperate zone.

RESERVOIR

Humans are the reservoir of infection

.

Nasopharyngeal carriage ranges from 1 to 50% and is responsible for infection to persist in a community

TRANSMISSION

Transmission is by air-borne droplets or from a nasopharyngeal carrier or less commonly from a patient through contact with respiratory droplets or oral secretions

. It is a delicate organism, dying rapidly on cooling or drying, and thus indirect transmission is not an important route. Travel and

migration, large population

movements

(

e.g

.

pilgrimages

, and overcrowding (e.g. slums), facilitate the circulation of virulent strains inside a country or from country to country.

HOST FACTORS

In countries within the meningitis belt the

maximum incidence

is found in the age group

5–10 years

; but in

epidemics all age groups may

be affected

. In institutions such as military

barracks, new

entrants and recruits usually have

higher attack

rates than those who have been in

long residence.

The

genetically determined inability to

secrete the

water-soluble glycoprotein form of the

ABO blood

group antigens into saliva and other

body fluids

, is a recognized risk factor for

meningococcal disease

. The relative risk of

non-secretors developing

meningococcal infection was found

to be

2.9 in a Nigerian study. The reasons why

nonsecretors

are

more susceptible are not known

.

Control

There are four basic approaches to the control

of meningococcal

infections:

■ the management of sick patients and

their contacts

;

■ environmental control designed to

reduce air-borne

infections;

■ immunization;

■ surveillance.

STREPTOCOCCAL INFECTIONS

Streptococcus

pyogenes

, group A haemolytic

streptococci can

invade various tissues of human skin

and subcutaneous

tissues, mucous membranes,

blood and

some deep tissues.

The common clinical

manifestations of

streptococcal infection include

streptococcal sore

throat, erysipelas, scarlet fever

and puerperal

fever. Some strains produce an

erythrogenic

toxin

which is responsible for the

characteristic erythematous

rash of scarlet fever. Rheumatic

fever and

acute glomerulonephritis

result from

allergic reactions to streptococcal infections

.

Epidemiology:

have a worldwide

occurrence, but the pattern of the distribution of streptococcal disease

varies from area to area.

Reservoir:

Humans are the reservoir

of infection; this includes

acutely ill and convalescent patients, as well as carriers, especially nasal carriers.

Transmission:

The

sources of infection are the infected discharges of sick patients, droplets, dust and fomites

.

The infection may be air-borne, through droplets, droplet nuclei or dust. It may be spread by contact or through contaminated milk.

HOST FACTORS

Although all age groups are liable to infection, children are particularly susceptible. Repeated attacks of tonsillitis and streptococcal sore throat are common but immunity is acquired to the

erythrogenic

toxin and thus it is rare to have a second attack of scarlet fever with the

scarlatinous

rash.

Control

The general measures for the control of

air-borne infections

are applicable. In addition, such

measures as

the

pasteurization of milk

and aseptic

obstetric techniques

are of

value.

Specific

chemoprophylaxis with penicillin

is indicated

for persons who have had rheumatic

fever and

for those who are liable to recurrent

streptococcal skin

infections. The penicillin can be

given orally

in the form of daily doses of penicillin V

.

RHEUMATIC FEVER

Rheumatic fever

is a complication of infection with group A haemolytic streptococci

.

The initial infection may present as a sore throat or may be subclinical; the onset of rheumatic fever is usually 2–3 weeks after the beginning of the throat infection

. Apart from fever, the patient may develop

pancarditis

, arthritis, chorea, subcutaneous nodules and erythema

marginatum

. Residual damage in the form of

chronic

valvular

heart disease may complicate clinical or subclinical cases of rheumatic fever; the complication is more liable to occur after repeated attacks.

Epidemiology

The disease has a

worldwide occurrence

. Although there is a falling incidence in the developed countries of the temperate zone, it is becoming a

more prominent problem in the overcrowded urban areas of some tropical and subtropical countries

, for example in South East Asia and the Middle East.

Rheumatic fever represents an allergic response in a small proportion of persons who have streptococcal sore throat. The factors that determine this sensitivity reaction are not known.

Control

The control of rheumatic fever involves the

control of

streptococcal infections in the

community

generally

and the

prevention of recurrences

by chemoprophylaxis

after recovery from an attack

of rheumatic

fever

.

PERTUSSIS (WHOOPING COUGH)

Infection with

Bordetella pertussis

leads to inflammation of the lower respiratory tract from the trachea to the bronchioles

. Clinically,

the infection is characterized by paroxysmal attacks of violent cough; a rapid successio

n

of coughs typically ends with a characteristic loud

, high-pitched inspiratory crowing sound – the so-called ‘

whoop

’.

Epidemiology:

The disease has a

worldwide distribution

but there is falling morbidity and mortality following immunization programmes.

Humans are the reservoir of infection

.

Transmission of infection may be air-borne or by contact

with freshly soiled articles. Children under 1 year old are highly susceptible and most deaths occur in young infants.

Control

INDIVIDUAL:

Sick children should be kept away from susceptible children

during the catarrhal phase of the whooping cough; isolation need not be continued beyond 3 weeks because the patient is no longer highly infectious even though the whoop persists.

VACCINATION:

Routine active immunization with

killed vaccine is highly recommended for all infants

. The pertussis vaccine is usually incorporated as a constituent of the triple antigen

DPT (diphtheria–pertussis– tetanus), which is used for the immunization of children starting from 2 to 3 months. It provides immunity for about 12 years.

DIPHTHERIA

This

disease is caused by infection

with

Corynebacterium

diphtheriae

(

Klebs

–

Loeffler

bacillus

). There

may be

acute infection of the

mucous membranes

of the tonsils, pharynx, larynx or

nose; skin

infections may also occur

and are of

particular importance

in tropical countries. Much

faucial

swelling

may be produced by the local

inflammatory reaction

and the membranous exudate in

the larynx

may cause respiratory obstruction. The

exotoxin which

is produced by the organism

may

cause

nerve

palsies

or

myocarditis

.

The

incubation period is 2–5 days.

Epidemiology

Although there is a worldwide occurrence of

the disease

, this once common epidemic disease

of childhood

is now

well controlled in most

developed countries

by routine immunization of infants.

There is

evidence to suggest that in some parts of the

tropics a

high proportion of the community acquires immunity

through subclinical infections, mainly

in the

form of cutaneous lesions

.

RESERVOIR

Humans

are the reservoir of infection; this

includes clinical

cases and also carriers

.

TRANSMISSION

The infective agents may be discharged from the nose and throat or from skin lesions. The transmission of the infection may be by:

■ air-borne infection;

■

direct contact;

■

indirect contact through fomites

;

■

ingestion of contaminated raw milk.

HOST FACTORS

All persons are liable to infection but

susceptibility to

infection may be modified by previous

natural exposure

to infection and immunization

.

The

newborn baby

may be protected for up to 6

months through

the

transplacental

transmission of

antibodies from

an immune

mother. The cutaneous lesions

which are often not recognized

produce immunization

of the host with low

morbidity.

Susceptibility

to infection

may be tested

by means

of the

Schick test

: a test dose of 0.2 ml

of

diluted

toxin

is injected intradermally into

one forearm

, with a similar injection of

toxin,

destroyed by

heat

, into the other forearm to serve as a

control.

Apositive

Schick test, consists of an

area of

redness 1–2

cm diameter

at the site of the test dose,

reaching its

maximum size in 3–4 days

, later fading into

a brown

stain. This positive reaction is confirmed

by the

absence of reaction at the site of the

control injection

.

Redness at both sides is recorded as

a

pseudoreaction

, and probably represents

nonspecific sensitivity

to some of the protein

substances in

the injection.

A negative Schick test is

recorded when

there is no redness at either injection

site. Both

the

pseudoreaction

and the negative

Schick test

are accepted as indicating resistance to

diphtheria infection.

Control

Antitoxin

should be given

promptly on making the clinical diagnosis and without awaiting laboratory confirmation.

Treatment with penicillin

or other antibiotics may be given in addition to, but not instead of, serum.

The patient should be isolated until throat cultures cease to yield toxigenic strains

. However, a patient is expected to be non-contagious within 48 hours of antibiotic administration. Isolation should be maintained until elimination of the organisms is demonstrated by two negative cultures obtained at least 24 hours apart after completion of antimicrobial therapy.

CONTACTS

Non-immune young children who have been

in direct

contact with the patient should be

protected by

passive immunization with antitoxic serum

and at

the same time,

active immunization with

toxoid

is

commenced.

Susceptible (Schick-positive)

adult contacts

should be protected with active

immunization and

a booster dose can be given to

immune (Schick-negative

) persons

. It is now

recommended that

all close contacts should receive antibiotic

prophylaxis to

be maintained for a week.

THE COMMUNITY

The

search for carriers and their treatment

with antibiotics

may be indicated in the special

circumstances of

an outbreak in a closed community

such as

a boarding school, but the major approach to

the control

of this infection is

routine active

immunization of

the susceptible

population

.

ACTIVE

IMMUNIZATION

Active immunization with

diphtheria toxoid

has proved

a reliable measure for the control of

this infection

. It is usually

administered in

combination with

pertussis vaccine and tetanus

toxoid (DPT

or triple antigen)

from the age of 2 to 3

months. A

booster dose of diphtheria toxoid is

recommended at

school entry and this may be given

in combination

with typhoid

vaccine.

The

following are the internationally

accepted interpretations

of the levels of circulating

diphtheria toxin

antibodies expressed in

IU/ml: 0.01

:

Susceptible 0.01–0.09

: Basic

protection 0.1

: Full

protection 1.0

: Long-term protection

FUNGAL INFECTIONS

HISTOPLASMOSIS

The

classical form of

histoplasmosis

due

to

Histoplasma

capsulatum

presents a variety of

clinical manifestations

. Infection is

mostly

asymptomatic

, being

detected only on immunological

tests.

On

first exposure there may be an acute

benign respiratory

illness

,

which tends to be

self-limiting

, healing

with or without calcification.

Progressive disseminated

lesions may occur with

widespread involvement

of the

reticulo

-endothelial

system; without

treatment this form may have a fatal

outcome

. The

incubation period is from 1 to 21

weeks.

Little

is known about its reservoir, mode

of transmission

or other epidemiological factors

.

Epidemiology

The infection is

endemic in certain parts of North, Central and South America, Africa and parts of the Far East.

RESERVOIR

The reservoir

is in soil, especially chicken coops, bat caves

and areas polluted with pigeon droppings.

TRANSMISSION

The infection is acquired by

inhalation of the spores

. Person to person transmission is rare.

HOST FACTORS

It is not clear why in some patients the infection progresses to severe disease.

Control

The main measure is to

avoid exposure to contaminated soil and caves

. Infected patients with significant disease can be treated with Amphotericin B.