Infectious Diseases: Clinical Correlations

Published on 18/02/2015 by admin

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Infectious Diseases

Clinical Correlations

I Sexually Transmitted Diseases (STDs)

1. Usually spread during asymptomatic period when partners are unaware of problem

2. Chlamydia trachomatis and human papillomavirus (HPV) infections are the most common STDs worldwide.

• C. trachomatis is often masked by coinfection with Neisseria gonorrhoeae.

B Table 30-1 summarizes diseases spread primarily by sexual contact.

TABLE 30-1

Sexually Transmitted Diseases

AIDS, acquired immunodeficiency syndrome.

When treating for N. gonorrhoeae, also treat for C. trachomatis.

II Urinary Tract Infections (UTIs) (Table 30-2)

TABLE 30-2

Bacteria Causing Urinary Tract Infections

Organism	Distinguishing Features	Notes
Escherichia coli	Gram negative, no capsule, red-black colonies on EMB agar	Most common cause of UTIs (50% to 80%)
Staphylococcus saprophyticus	Gram positive, coagulase negative, resistant to novobiocin	Second most common cause of UTIs in young women (10% to 30%)
Proteus mirabilis	Gram negative, urease positive, swarming growth on agar	Associated with struvite urinary stones
Klebsiella pneumoniae	Gram negative, nonmotile, prominent capsule, large mucoid colonies	Usually in catheterized patients
Enterobacter species	Gram negative, motile, capsule, moist colonies, often drug resistant	Usually in immunocompromised patients
Pseudomonas aeruginosa	Gram negative, oxidase positive, fruity odor, blue-green pigment	Usually in patients with kidney stones, chronic prostatitis, or a catheter
Enterococcus faecalis	Gram positive, variable hemolysis, salt tolerant (6.5% NaCl)	Usually in immunocompromised or catheterized patients

UTI, urinary tract infection.

• Most common causes of nosocomial UTIs are Escherichia coli, Enterococcus species, and Pseudomonas aeruginosa.

A Cystitis (lower UTI)

1. Most commonly caused by E. coli.

2. Higher incidence in women

3. Dysuria, frequency, urgency, suprapubic pain

4. Not accompanied by bacteremia

E. coli is the most common UTI.

B Pyelonephritis (upper UTI): flank pain, fever, chills, dysuria

1. Results from ascension of bacteria from infected bladder

2. May be accompanied by bacteremia

C Genitourinary tract pathogens that are not sexually transmitted

• Candida albicans (vulvovaginitis), Staphylococcus aureus (toxic shock syndrome), and various organisms that infect the urinary tract.

III Infectious Diarrheas (Tables 30-3 and 30-4)

TABLE 30-3

Major Infectious Agents of Diarrhea

cAMP, cyclic adenosine monophosphate; cGMP, cyclic guanosine monophosphate; I, inflammatory; I-I, inflammatory, invasive; NI, noninflammatory.

TABLE 30-4

Food Sources of Bacterial Infections

Food	Bacteria
Poultry	Salmonella enteritidis, Campylobacter species
Raw eggs	Salmonella enteritidis
Dairy products	Listeria monocytogenes, Brucella species, Mycobacterium bovis
Shellfish	Vibrio species
Reheated rice	Bacillus cereus
Undercooked beef	Escherichia coli O157:H7, B. cereus, Brucella species, C. perfringens
Picnic foods (mayonnaise, custard, salted meats)	S. aureus toxin mediated

A Distinguishing features of three types

1. Noninflammatory diarrhea is watery

• Site of pathology: small intestine

• Bacteremia and fecal leukocytes not present

• Mediated by bacterial toxins and viruses

2. Inflammatory diarrhea is watery or bloody

• Lesion in colon

• Fever and fecal leukocytes common

• Bacteremia uncommon

3. Inflammatory, invasive diarrhea is bloody

• Lesion in Peyer patches

• Fever prolonged

• Bacteremia and fecal leukocytes common

B Typical time of onset after infection by various agents

1. 1 to 6 hours

• S. aureus and Bacillus cereus (preformed toxin)

2. 8 to 16 hours

• Clostridium perfringens and B. cereus (toxin produced after infection)

3. 24 to 48 hours

• Norwalk virus and rotavirus

• E. coli (ETEC) and Vibrio cholerae (toxin produced after infection)

5. More than 24 hours

• E. coli (EHEC); Shigella, Salmonella, and Campylobacter species; Yersinia enterocolitica, Entamoeba histolytica, and Giardia lamblia (adherence, growth, invasion)

IV Pneumonia (Table 30-5)

TABLE 30-5

Primary Causes of Pneumonia by Age Group

Streptococcus pneumoniae and Haemophilus influenzae cause typical pneumonia; other organisms may cause atypical pneumonia.

RSV, respiratory syncytial virus.

A Clinical presentation

• Abrupt onset, high fever (>39°C), productive cough with blood-tinged sputum, chest pain, consolidated “whited-out” infiltrate throughout lower lobe on chest radiograph

• Streptococcus pneumoniae, Haemophilus influenzae, and S. aureus

• Slow onset of nonproductive cough, moderate fever (<39°C), headache, sore throat, gastrointestinal symptoms, patchy infiltrates on chest radiograph

• Mycoplasma pneumoniae, Chlamydophila species, Legionella species, viruses, and fungi

B Bacterial pneumonia

1. Community acquired

• Streptococcus pneumoniae, H. influenzae, M. pneumoniae, Chlamydophila pneumoniae, Legionella species, S. aureus

• S. aureus and gram-negative rods including E. coli, Klebsiella pneumoniae, and P. aeruginosa

C Viral pneumonia

1. Respiratory syncytial virus (RSV), parainfluenza virus, and influenza virus are most common causes.

2. Bacterial superinfection, usually by S. aureus, often complicates these infections.

D Fungal pneumonia

• Immunocompromised patients are most at risk for atypical, chronic pneumonia due to fungi.

1. Pneumocystis jiroveci (carinii) causes potentially fatal pneumonia, in acquired immunodeficiency syndrome (AIDS) patients.

2. Histoplasma capsulatum, Coccidioides immitis, and Blastomyces dermatitidis can cause pneumonia in both immunocompetent and immunocompromised individuals.

V Meningitis and Encephalitis (Table 30-6)

TABLE 30-6

Central Nervous System Disease

AIDS, acquired immunodeficiency disease; HSV, herpes simplex virus; HTLV-1, human T lymphotropic virus type 1; PML, progressive multifocal leukoencephalopathy; SSPE, subacute sclerosing panencephalitis.

^*Most common cause of disease.

• Analysis of cerebrospinal fluid usually can distinguish bacterial, viral, and fungal causes of meningitis (Table 30-7).

TABLE 30-7

Analysis of Cerebrospinal Fluid in Meningitis

N, normal values; PMNs, polymorphonuclear leukocytes; single arrow, increase (↑) or decrease (↓); double arrows, marked increase or decrease.

A Acute bacterial meningitis

1. In adults: Streptococcus pneumoniae and Neisseria meningitidis are most common causes in immunocompetent individuals.

• Terminal complement deficiency (C5 -C9) predisposes to N. meningitidis infection.

• Meningitis due to Listeria monocytogenes is seen in immunocompromised patients and the elderly.

• Group B streptococci, E. coli, and Listeria species are major causes.

• H. influenzae B is a common cause, as well as Strep pneumoniae and N. meningitidis.

• Hib vaccine has almost eliminated H. influenzae meningitis cases.

B Viral (aseptic) meningitis

1. Enteroviruses (especially Coxsackie viruses) and herpes simplex virus are the most common causes.

2. Mumps virus and lymphocytic choriomeningitis virus (LCMV) are less common causes.

3. LCMV in immunocompromised patients

C Chronic meningitis

• Mycobacterium tuberculosis and fungi (e.g., Cryptococcus neoformans and C. immitis) are common causes.

D Encephalitis

• Herpes simplex virus

• Arboviruses (arthropod borne)

• Measles, mumps, rabies

E Other diseases

1. Progressive multifocal leukoencephalopathy—JC virus in immunocompromised patients

2. Subacute sclerosing panencephalitis—defective measles virus

3. Spongiform encephalopathy (Creutzfeldt-Jakob disease)—prions

4. Cysticercosis—Taenia solium

5. Brain abscess

• Anaerobic streptococci, staphylococci, bacteroides, and other bacteria; Aspergillus species, Toxoplasma gondii (immunosuppressed)

VI Arthropod-Associated Diseases (Table 30-8)

TABLE 30-8

Arthropod-Associated Diseases

^*Outbreaks and spread of the vector may go beyond the indicated regions.

• Arthropods may act as simple vectors and, in some cases, also as intermediate hosts in the transmission of human pathogens.

• Humans are most likely to contract these diseases when they enter the native habitat of the vectors.

VII Common Infectious Causes of Other Conditions

A Ear infections

1. Otitis media, sinusitis in children

• Strep pneumoniae, H. influenzae, Moraxella catarrhalis, anaerobes

2. Otitis externa (swimmer’s ear)—P. aeruginosa

B Osteomyelitis

1. S. aureus in most individuals (especially children)

2. Salmonella in individuals with sickle cell disease

C Congenital, neonatal complications

• TORCHES—toxoplasma, rubella virus, cytomegalovirus, herpes simplex virus, syphilis

D Endocarditis

• Rapid onset; usually involves previously normal valves

• S. aureus (most common cause) and Strep pneumoniae

• Slow onset over months; usually involves diseased, abnormal, or prosthetic valves

• Viridans streptococci (most common) and Enterococcus species

• Staphylococcus epidermidis and S. aureus (particularly involving prosthetic valves)

• HACEK organisms—Haemophilus, Actinobacillus, cardiobacterium, Eikenella, Kingella

E Toxic shock and septic shock

1. Toxic shock is caused by superantigen activation of T cells and massive cytokine release.

• S. aureus TSST, Streptococcus pyogenes erythrogenic toxin A or C

2. Sepsis induces systemic release of acute phase cytokines

• Toll-like receptor–mediated response of leukocytes to presence of bacterial cell wall components in blood

• Usually gram-negative bacteria

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