Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5470_Библиотеки_им_академика_М_И_Перельмана.pdf
173Introduction to Microbiology
Aims of Epidemiology
1. To determine the incidence/prevalence of the disease in
the community.
2. To determine the causative factors.
3. To understand how to prevent or control the disease.
Concept of Epidemiology
The three main components of epidemiology are given below:
1. Disease frequency: The study of disease frequency refers
to the calculation of rates or ratios (e.g. prevalence rate,
incidence rate, death rate, etc.). These rates and ratios are
important for comparing the frequency of occurrence of
disease in different populations or subgroups of the same
population concerning suspected causal factors. Such
comparisons give important information about disease
etiology.
2. Distribution of disease: An important function of
epidemiology is to study the trends in the occurrence of the
disease concerning time, place, and person. That is, the
epidemiologist examines whether there has been an
increase or decrease in disease over the years; whether
there is a higher concentration of disease in one geographic
area than others; and whether the disease occurs more
often in men or a particular age-group.
3. Determinants of disease: A unique feature of epidemio-
logy is to test etiological hypotheses and identify the
underlying causes or risk factors of disease.
Objectives of Epidemiology
The main aim of epidemiology is to minimize or eradicate the
disease or health problem. To achieve this, epidemiology has
the following objectives:
a. To describe the distribution and magnitude of disease
problems in human populations.
b. To identify etiological factors/risk factors in the patho-
genesis of disease.
174 Social Pharmacy
c. To provide the data essential for the planning,
implementation, and evaluation of services aimed at
preventing, controlling, and treating disease.
Applications and Uses of Epidemiology
1. To study the time trends of disease in the population.
2. To identify the health problems in a community.
3. To estimate the degree of risk of the disease in a popu-
lation.
4. To identify syndromes.
5. To study the natural history of disease.
6. To identify the causes and risk factors of a disease.
7. To manage the health services efficiently.
Terms Used in Epidemiology
Infection: It is the entry and development of microorganisms
in the body.
Infestation: Presence of arthropod vector on the body or
clothes.
Contamination: Presence of an infective agent/on any
surface or non-living things.
Infectious disease: Any disease, which happens due to an
infectious agent or infectious etiology, e.g. rheumatic fever,
cervical cancer, peptic ulcer.
Contagious disease: Any disease that is transmitted by direct
touch, e.g., dermatitis scabies.
Communicable disease: Diseases, that may be transmitted
via any mode of transmission, e.g. tuberculosis
Epidemic: An epidemic is a sudden or gradual rise in the
number of cases of the disease, which is more than 80% of the
expected frequency. It may be classified as:
1. Common source (point source) epidemics:
a. Single exposure epidemics
b. Multiple exposure epidemics
2. Propagated epidemics: There is an exponential increase in
number of cases. There will be an abrupt rise in the number
175Introduction to Microbiology
of cases. There is person-to-person transmission. Cases
occur at more than one incubation period. Secondary
waves are seen. A decline in cases is seen with herd
immunity if a susceptible population is unavailable
(vaccination)/decreased density of the population, e.g. the
COVID-19 epidemic.
Pandemic: A pandemic is a global epidemic, i.e., an epidemic
that spreads to more than one continent or worldwide.
Endemic: (En = in; demos = people). It refers to the constant
presence of a disease or infectious agent within a given
geographic area or population group, e.g., the common cold.
An endemic disease may burst into an epidemic (e.g., typhoid
fever).
Mode of transmission: It refers to how an infectious agent/
pathogen can be transferred from one person, object, or animal,
to another. Viruses, bacteria, parasites, or fungi can spread
infectious diseases. There are two different modes of
transmission of diseases:
A. Direct transmission: In this, the pathogen is transmitted
directly from an infected person.
B. Indirect transmission: In this, the pathogens are trans-
mitted from the infected person through vectors such as
flies, mosquitoes, ticks, dogs, etc.
Table 4.2: Comparison of single and multiple exposure epidemics
S. Single exposure epidemics Multiple exposure epidemics
No.
1. All the cases occur within Multiple exposures occur from
one incubation period after the point source. There is no
a single exposure person-to-person transmission.
2. The average incubation Cases occur at >1 incubation
period corresponds to the period
median incubation period
3. There is a rise in the number There is a rise in the number of
of cases followed by a fall cases but there is no fall (persis-
tence): Hyper endemic state
4. Only one wave is seen, i.e. Secondary waves are seen
the primary wave
176 Social Pharmacy
A. Direct Transmission
Person to person: When a person comes in direct contact
with an infected person. Diseases like scabies and dermatitis
can be transmitted this way.
Transplacental: Pregnant mother can also transmit
infectious diseases to their unborn child via the placenta.
Droplet transmission: The droplets formed during sneezing,
speaking, and coughing by an infected person can spread
infections, e.g. tuberculosis.
Spread by skin: Infections spread when the skin of an
infected person comes in contact with the skin of the other
person, e.g. chickenpox, conjunctivitis, head lice, ringworm,
etc.
Spread through body fluids or blood: Diseases spread when
the body fluids or blood of an infected person come in contact
with the mucous membrane or blood stream of an uninfected
person, e.g. hepatitis, HIV, cytomegalovirus infections, etc.
spread through semen and vaginal fluids, saliva, breast milk,
urine, etc.
Soil: Soil is a reservoir for many disease-causing organisms,
e.g. soil can transmit helminthic infections and tetanus.
B. Indirect Transmission
1. Airborne transmission: Some infectious agents (patho-
gens) remain suspended in the air for a long period. These
pathogens might attack the immune system of a person in
contact, e.g., measles, chickenpox, influenza, COVID-19,
tuberculosis.
2. Contaminated objects: The objects around us may act as
vectors for diseases if contaminated with pathogens.
Contaminated fomites and medical supplies can also
spread infections.
3. Vector-borne diseases: Some infectious agents are
transmitted by blood-sucking insects. The insects feed on
hosts such as birds, animals, and humans and carry infec-
tious agents from them. These infections are transmitted to
some new host. Malaria, plague, and lyme disease are
vector-borne diseases.
177Introduction to Microbiology
4. Food and drinking water: Improperly canned, under-
cooked food and contaminated water are the main sources
of infections, e.g. water-borne diseases (cholera, typhoid,
gastroenteritis).
An overview of different modes of disease transmission is
given in Table 4.3.
Table 4.3: Different modes of disease transmission
Disease Modes of disease Diseases caused
transmission transmission
Direct Person to person
transmission Transplacental Gonorrhoea
Droplet transmission Tuberculosis
Skin Conjunctivitis, chickenpox
Body fluids or blood HIV, hepatitis
Soil
Indirect Airborne transmission Measles, influenza
transmission Contaminated objects Cold, syphilis
Vector-borne transmis- Malaria, lyme
sion disease
Transmission through Cholera, diarrhea
food and water
Transmission through Rabies, anthrax
animals
Environmental factors Hookworm, legionnaires’
disease
Fig. 4.3: Modes of disease transmission
Outbreak: It is a sudden or abrupt rise in the number of
cases of a disease within a particular area is known as an
outbreak.
178 Social Pharmacy
Quarantine: Quarantine separates and restricts the
movement of people who were exposed to a contagious disease
to see if they become sick.
Isolation: It is the complete separation of sick people with a
contagious disease from people who are not sick.
Incubation period: It is the period between exposure to an
infectious agent and the development of symptoms.
Contact tracing: It is the practice of identifying, notifying,
and monitoring individuals who have recently been in close
contact with a person having an infectious disease.
Morbidity: It refers to a diseased state, disability, or poor
health due to any cause, e.g., heart disease, diabetes, and
obesity. Morbidity can be measured as the incidence and
prevalence of disease.
Common morbidity indicators are:
i. Incidence rate: The incidence rate is the total number
of new cases per unit of time in a defined population.
ii. Prevalence rate: Prevalence rate is the total number of
all cases in a defined population, usually expressed as
per 100 populations.
Prevalence = Incidence × duration
Prevalence decreases while incidence remains the same if
there is a better cure for a non-communicable disease.
Prevalence and incidence both decrease if there is a better
cure for a communicable disease.
Mortality: It refers to the number of deaths in one period of
time or one place. The crude death rate, cause-specific death
rate, proportional mortality rate, case fatality rate, infant
mortality rate, maternal mortality rate, child mortality rate, etc.
are common mortality indicators.
i.
Number of deaths due to specific cause
Cause specific death rate 1000
Mid year population
ii.
Number of deaths due to specific cause
Cause specific death rate 1000
Mid year population
iii.
Number of deaths due to
certain disease
Pr oportional mortalit
y
rate 1000
Total deaths
179Introduction to Microbiology
iv.
Number of deaths due to certain disease
Case fertilit
y
rate 1000
Total cases of that disease
v.
Number of deaths of children below
1 year of age during a year in the area
Infant mortalit
y
rate 1000
Number of live births registered or
estimated during the year in the area
vi. Maternal mortality rate: It accounts for deaths during antenatal, natal, and
postnatal.
vii.
Number of deaths registered or estimated
of children between 1 to 4 years of age
duringayearinthearea
Child mortalit
y
rate 1000
Midyearpopulationof1to4yearsof
age group
Respiratory Tract Infections
a) Chickenpox (Varicella)
Causative organism: Varicella zoster virus (VZV).
Incubation period: 14 to 16 days.
Epidemiology: Chickenpox is as old as smallpox. It is a highly
contagious viral disease. It occurs worldwide sporadically,
endemically, or epidemically. Humans are the only known
reservoir for VZV. Chickenpox may be life-threatening in
immunosuppressed patients, neonates, and smokers. The
epidemiology of chickenpox appears to be changing. There has
been an unexplained upward shift in the age distribution of
cases over the last 20 years.
Epidemiological determinants:
Agent factors:
1. The source of infection is usually a case of chickenpox.
2. Scabs are not infective.
3. Vesicle fluids are infective.
4. The period of communicability is 1 to 2 days before and
4 to 5 days after the onset of rash.
5. The secondary attack rate is 85 to 90%.
Host factors:
1. Age: It occurs mostly in children under the age of
10 years.
2. Immunity: The disease confers lifelong immunity.
180 Social Pharmacy
3. Pregnancy: Infection in the first 20 weeks of pregnancy
has higher chances of congenital varicella syndrome.
Environmental factors:
1. Chickenpox shows a seasonal trend and mostly occurs
in winter and spring from January to April.
2. Viruses can survive for 24 to 48 hours outside the body.
3. The virus is easily destroyed by chemical solvents and
detergents.
Mode of transmission: The infected person is the main source
of infection. It is an airborne disease, which is transmitted from
person to person easily by :
1. Droplet transmission, mostly by cough and sneezing
2. Transplacental mode
3. Direct contact, and
4. Infected articles.
Clinical features: Itchy vesicular skin rash accompanied by
fever, loss of appetite, headache, and malaise. Scabs develop
after 4 to 5 days and are non-infective.
The clinical spectrum of chickenpox may vary from child to
child. The clinical course of chickenpox may be divided into
two stages:
(i) Pre-eruptive stage: Onset is sudden with mild or
moderate fever, pain in back shivering, and malaise.
This stage lasts for about 24 hours in adults.
(ii) Eruptive stage: The rashes come on the day the fever
starts. It starts in trunks and spreads to the whole body
except palms and soles. The rash shows pleomorphism
(i.e., all different stages of the rash may be seen
simultaneously at one time in the same area). Scabs
develop around 4 to 5 days after the rash appears and
are non-infective.
Prevention and control:
1. Avoid direct contact with an infected person.
2. Complete isolation of patients for about 6 days.
3. Disinfection of articles soiled by nasal and throat
discharges.
181Introduction to Microbiology
4. Maintenance of good hygiene and daily cleaning of skin
with warm water.
5. Passive immunization by V-zoster immunoglobulin
(VZIG).
6. Active immunization by live attenuated Varicella
vaccine (OKA vaccine).
Treatment: The disease is self-limiting and hence no
treatment is required. The immune system clears the virus from
the body. Usually, the treatment is symptomatic and calamine
lotion is applied topically. The patient suffering from serious
complications like pneumonia, hemorrhage, and encephalitis
needs hospitalization. Oral therapy with acyclovir (20 mg/kg/
dose; maximum: 800 mg/dose) is given in four doses per day
for five days.
b. Measles
Measles is a highly infectious viral disease.
Causative organism: RNA paramyxovirus belonging to the
genus Morbillivirus of the family Paramitoviridae is the
causative agent.
Incubation period: 9–12 days.
Epidemiology: Measles is endemic all over the world and is
a leading cause of childhood morbidity and mortality. Almost
all people suffer from it once.
Epidemiological determinants:
Agent factors:
1. The source of infection is a case of measles.
2. Secretions of the nose, throat, and respiratory tract of a
case of measles during the prodromal (period after
incubation and before the characteristic symptoms of
infection occur) period and the early stages of the rash
are infective.
3. The period of communicability is 4 days before and
4 days after the appearance of the rash.
Host factors:
1. Age and sex: It occurs mostly in children of both sexes
between the ages of 6 months to 3 years in developing
182 Social Pharmacy
countries and greater than five years of age in deve-
loped countries.
2. Immunity: The disease confers lifelong immunity.
3. Nutritional status: Malnourished children are more
affected.
Environmental factors:
1. Measles does not show a seasonal trend and most
epidemics in India occur in winter and spring from
January to April.
2. The virus cannot survive outside the human body for
any length of time but retains infectivity when stored
at sub-zero temperatures.
Mode of transmission: It spreads from the infected person
mainly by:
1. Coughing and sneezing.
2. Close personal contact or direct contact with infected
nasal or throat secretions.
Clinical features: There are three stages of measles infection
namely:
1. Prodromal stage: It lasts 3 to 5 days. It is characterized
by:
i. Fever
ii. Running nose
iii. Cough
iv. Diarrhea
v. Koplik’s spots in buccal mucosa near the first or
second lower molars appear 2 to 3 days before
rashes.
2. Eruptive stage: This phase is characterized by the onset
of a maculopapular rash that starts behind the ears and
extends down the body. It takes 2 to 3 days to spread to
the whole body and takes another 4 to 5 days to
disappear. Peak viral shedding occurs 2 to 5 days after
the onset of the rash.
3. Post-measles stage: Presents with weakness, and
weight loss. The most common associated feature of
measles (apart from fever and rash) is diarrhea.