Download MBBS (Bachelor of Medicine, Bachelor of Surgery) General Medicine 2022 PPT 4 Gn Infections Part II Lecture Notes
Infectious diseases
4/5th Semester Classes on Infectious Diseases, 8-9AM, Tuesdays (LT-1)
Topics
1
Approach to Infectious Diseases and their prevention
2
Antibiotic stewardship practices
3
Community-Acquired Infections
4
Health Care?Associated Infections
5
Gram-Positive Bacteria (part-1)
6
Gram-Positive Bacteria (part-2)
7
Gram-Negative Bacteria (part-1)
8
Gram-Negative Bacteria (part-2)
9
Spirochetal Diseases
10
Diseases Caused by Atypical/Miscellaneous Bacterial Infections
11
Revision-cum-exam on bacteria (Must to know type)
12
Infections Due to DNA Viruses
1
13
Infections Due to RNA Viruses (part 1)
14
Infections Due to RNA Viruses (part 2)
15
HIV/AIDS ? part 1
16
HIV/AIDS ? part 2
17
Fungal Infections
18
Parasitic Infections (part 1)
19
Parasitic Infections (part 2)
20
Revision-cum-exam on Virus, Fungal, and Parasite (Must to know type)
ENTEROBACTERIACEAE
(E. coli, Klebsiella, Proteus, Enterobacter)
In healthy humans, E. coli is the predominant species of gram-negative
bacilli (GNB) in the colonic flora; Klebsiella and Proteus are less prevalent
Multiple bacterial virulence factors are required for the pathogenesis
Certain strains of E. coli are capable of causing diarrheal disease
ExPEC strains are the most common enteric GNB to cause community-acquired and
health care?associated bacterial infections (Al age groups, al types of hosts, and nearly
al organs and anatomic sites)
Humans are the major reservoir [except for STEC/EHEC]
Transmission occurs predominantly via contaminated food and water
for ETEC, STEC/EHEC/STEAEC, EIEC, and EAEC and by person-to-
person spread for EPEC (and occasionally STEC/EHEC/STEAEC)
Except in the cases of EHEC and EAEC, disease occurs primarily in
developing countries
Distinguish noninflammatory (mainly by ETEC, EPEC, and DAEC) from
inflammatory diarrhea (suggested by grossly bloody or mucoid stool
or a positive test for fecal leukocytes)
Definitive diagnosis generally is not necessary except for STEC
The mainstay of treatment for all diarrheal syndromes is replacement
of water and electrolytes, especially for STEC/EHEC/STEAEC infection
where antibiotics may increase the incidence of HUS
If diarrhea persists for >10 days despite treatment, Giardia or
Cryptosporidium should be sought
Person-to-person spread is the predominant mode of acquisition of
Klebsiel a
cKP Causes pneumonia, UTI, abdominal infection, intravascular device
infection, surgical site infection, soft tissue infection, and subsequent
bacteremia
hvKP (of Asian origin) infection distinguished from traditional infections
due to cKP by
(1) presentation as community-acquired pyogenic liver abscess
(2) occurrence in patients lacking a history of hepatobiliary disease,
and
(3) a propensity for metastatic spread to distant sites
Urine samples with unexplained alkalinity should be cultured for Proteus,
and identification of a Proteus species in urine should prompt
consideration of an evaluation for urolithiasis
Enterobacter/citrobacter/serratia/morganel a/edwardsiel a causes a
spectrum of extraintestinal infections similar to other GNB
SALMONELLA
Two species: Salmonella enterica and Salmonella bongori
Serotyping is based on the somatic O antigen (lipopolysaccharide cellwall components),
the surface Vi antigen (restricted to S. typhi and S. paratyphi C), and the flagellar H
antigen
The growth of serotypes Salmonel a typhi and Salmonel a paratyphi is restricted to human
hosts, remaining serotypes (nontyphoidal Salmonella, or NTS) can colonize the
gastrointestinal tracts of a broad range of animals, reptiles, birds, and insects
Ingestion in contaminated food or water with the ingested dose as determinant of
incubation period and disease severity
Conditions that decrease either stomach acidity or intestinal integrity increase
susceptibility to infection
Once reach the smal intestine, they penetrate the mucus layer of the gut, traverse the
intestinal layer through phagocytic microfold (M) cells that reside within Peyer's patches,
phagocytosed by macrophages but in a protective manner, and then via the lymphatics
colonize reticuloendothelial tissues
In contrast to enteric fever, NTS gastroenteritis is characterized by massive
polymorphonuclear leukocyte infiltration into both the large- and smal -bowel mucosa
Enteric (typhoid) fever is a systemic disease characterized by fever and
abdominal pain and caused by dissemination of S. typhi or S. paratyphi
Most commonly, food-borne or waterborne transmission results from fecal
contamination; Sexual transmission between male partners has been
described; Health care workers occasionally acquire too
IP; 10?14 days but ranges from 5 to 21 days
Risk factors include
1. contaminated water or ice,
2. flooding,
3. food and drinks purchased from street vendors,
4. raw fruits and vegetables grown in fields fertilized with sewage,
5. ill household contacts,
6. lack of hand washing and toilet access, and
7. evidence of prior Helicobacter pylori infection
It is estimated that there is one case of paratyphoid fever for every four
cases of typhoid fever
SYMPTOMS
SIGNS
Fever (>75%)
coated tongue (51?56%),
headache (80%)
relative bradycardia at the peak of high
anorexia (55%)
fever (<50%)
chills (35?45%)
rose spots (30%),
Abdominal pain (30-40%)
splenomegaly (5?6%),
cough (30%)
abdominal tenderness (4?5%)
sweating (20?25%)
hepatosplenomegaly (3?6%),
myalgias (20%),
epistaxis,
nausea (18?24%),
vomiting (18%),
diarrhea (22?28%)
Constipation (13?16%)
malaise (10%)
arthralgia (2?4%).
The development of severe disease (which occurs
in ~10?15% of patients) depends on host factors,
strain virulence and inoculum, and choice of
antibiotic therapy
? Gastrointestinal bleeding (10?20%)
? Intestinal perforation (1?3%)
? Neurologic manifestations (2-40%)
Up to 10% of untreated patients excrete S. typhi in the feces for up to 3 months, and 1
?4% develop chronic asymptomatic carriage, shedding S. typhi in either urine or stool
for >1 year
The definitive diagnosis of enteric fever requires the isolation of S. typhi or S. paratyphi
from blood, bone marrow, intestinal secretions,(THESE 3 IN COMBINATION POSITIVE
>90%) other sterile sites, rose spots, and stool
Serologic tests, including the classic Widal test for "febrile agglutinins," and rapid tests
to detect antibodies to outermembrane proteins have lower positive predictive
values than blood culture
Two typhoid vaccines:
(1)Ty21a, (given on days
1, 3, 5, and 7, with a
booster every 5 years);
(2)Vi CPS, (given in a
single dose, with a
booster every 2 years)
cumulative efficacy was
48% for Ty21a at 2.5?3.5
years and 55% for Vi CPS
at 3 years
SHIGELLA
Shigella cannot be distinguished from Escherichia coli by DNA hybridization and
remains a separate species only on hstorical and clinical grounds
Unlike E. coli, is nonmotile and does not produce gas from sugars
Human intestinal tract represents the major reservoir
Bacteria are transmitted most efficiently by the fecal-oral route via hand
carriage, rarely by flies and sexually
Highest prevalences in the most impoverished areas
Shigellosis typically evolves through four phases:
1. Incubation (1?4 days),
2. Watery diarrhea,
3. Dysentery - dysentery--a clinical syndrome of fever, intestinal cramps, and frequent
passage of small, bloody, mucopurulent stools
4. Postinfectious phase ? Reactive arthritis, toxic megacolon, and HUS (in developing
countries)
Ciprofloxacin is recommended as first-line treatment; others like ceftriaxone,
azithromycin, pivmecillinam, and some fifth-generation quinolones
VIBRIO
Cholera now refers to disease caused by V. cholerae serogroup O1 or O139--
i.e., the serogroups with epidemic potential
Responsible for seven global pandemics and much suffering over the past two
centuries
In nature, vibrios most commonly reside in tidal rivers and bays under conditions
of moderate salinity; They proliferate in the summer months
Cholera is predominantly a pediatric disease in endemic areas, but it affects
adults and children equal y when newly introduced into a population
Cholera toxin, toxin-coregulated pilus, and several other virulence factors are
coordinately regulated by ToxR With IP 24- to 48-h
Some individuals are asymptomatic or have only mild diarrhea; others present
with the sudden onset of explosive and life-threatening diarrhea (cholera
gravis); "rice-water" stool WITH absent fever; Complications derive exclusively
from the effects of volume and electrolyte depletion
Clinical suspicion of cholera can be confirmed by the identification in stool
Treatment; first and foremost requires fluid resuscitation with macrolides (DOC)
PSEUDOMONADS (an inability to ferment lactose)
Pseudomonas, Burkholderia, and Stenotrophomonas
The pathogenicity is based on opportunism with the exceptions (melioidosis by
Burkholderia pseudomallei and glanders by B. mallei)
P. aeruginosa remains the most common contributing factor to respiratory
failure in Cystic Fibrosis
B. cepacia gained notoriety as the cause of a rapidly fatal syndrome of
respiratory distress and septicemia (the "cepacia syndrome") in CF patients
Cytotoxic chemotherapy, mechanical ventilation, and broad-spectrum
antibiotic therapy probably paved the way for colonization and infection
P. aeruginosa is found in most moist environments; infection Often occurs
concomitantly with host defense compromise
Of the common gram-negative bacteria, no other species produces such a
large number of putative virulence factors
Among gram-negative bacteria, it probably produces the largest number of
substances that are toxic to cells and thus may injure tissues
P. aeruginosa causes infections at almost all sites in the body but shows a rather
strong predilection for the lungs
Bacteremia; only point differentiating this entity from gram-negative sepsis of other
causes may be ecthyma gangrenosum, which occur almost exclusively in markedly
neutropenic patients and patients with AIDS
Combination therapy became the standard of care, recently newer
antipseudomonal drugs (colistin, tigecycline, cefepime) can be used as
monotherapy
ACINETOBACTER
Acinetobacter baumannii is particularly formidable because of its propensity to
acquire antibiotic resistance determinants
Contrary to previous thought of nonmotile characteristic it demonstrate motility
under certain growth conditions
Widely distributed in nature, like water, soil, on vegetables, a component of the
skin flora, and sometimes a contaminant in blood samples
Colonizes patients exposed to heavily contaminated hospital environments or
to the hands of health care workers
It must be considered in the dif erential diagnosis of hospital-acquired
pneumonia, central line?associated bloodstream infection, posttraumatic
wound infection in military personnel, and postneurosurgical meningitis
It should be suspected when plump coccobacil i are seen in Gram's-stained
samples
Only sulbabctam, cotrimoxazole, carbapenams, amikacin, tigecycline, colistin
are possible treatment
HELICOBACTER
It colonizes the stomach in ~50% of the world's human population, essentially
for life unless eradicated by antibiotic treatment
Humans are the only important reservoir
Lifelong colonization may offer some protection against complications of
gastroesophageal reflux disease (GERD), including esophageal
adenocarcinoma
Treatment against the organism prevent/treat PUD and low-grade gastric MALT
lymphoma, however, no benefit in the treatment of gastric adenocarcinoma
Nongastric (intestinal) Helicobacter species can cause clinical features
resembling those of Campylobacter infections
Prevalence varies with age: H. pylori is usually acquired in childhood, The age
association is due mostly to a birth-cohort effect
Combination of factors lead to disease state: bacterial strain dif erences, host
susceptibility to disease, and environmental factors
Whether or not the ulcers are currently active, H. pylori should be eradicated in
patients with documented ulcer disease to prevent Relapse
Overall most treatment of asymptomatic H. pylori carriage is given without a firm
evidence base
Test-and-treat has emerged as a common clinical practice
CAMPYLOBACTER
Campylobacter, Arcobacter, and Helicobacter
It is more common than that due to Salmonel a and Shigel a combined
Although acute diarrheal illnesses are most common, these organisms may cause
infections in virtually al parts of the body, especially in compromised hosts, and these
infections may have late nonsuppurative sequelae (Reactive A, GBS)
The human pathogens fall into two major groups:
those that primarily cause diarrheal disease (C. jejuni mainly)
those that cause extraintestinal infection (C. fetus mainly)
Transmitted to humans in raw or undercooked food products or through direct contact
with infected animals
The symptoms of Campylobacter enteritis are not sufficiently unusual to distinguish this
illness from that due to Salmonel a, Shigel a, Yersinia, and clostridium (inflammatory
bacterial diarrhea)
Diagnosis of inflammatory bowel disease should not be made until Campylobacter
infection has been ruled out
Indications for therapy include high fever, bloody diarrhea, severe diarrhea, persistence
for >1 week, and worsening of symptoms
A 5- to 7-day course of erythromycin (250 mg orally four times daily) is DOC
Thank you
This post was last modified on 05 April 2022