Infectious Diseases: Causes, Symptoms, Diagnosis and Treatment

Gastrointestinal Infections

Infectious gastroenteritis and bacterial contamination of foods: Salmonella enterica (eggs, meat), Clostridium perfringens (stews), Staphylococcus aureus (salted foods), Clostridium botulinum (fish).

Infections from water and food-borne microorganisms: Vibrio cholerae (cholera), E. coli (diarrhea, hemorrhagic colitis), Campylobacter jejuni (abdominal cramps, diarrhea), rotavirus (infectious diarrhea).

Upper and Lower Respiratory Tract Infections

Respiratory tract infections: caused by bacteria and viruses.

Upper Respiratory Tract

Pharyngitis: caused by viruses or bacteria (Streptococcus pyogenes, tonsillitis). Diagnosis: antigen detection and culture.

Common cold: caused by viruses (rhinovirus).

Diphtheria: Corynebacterium diphtheriae produces a toxin that destroys epithelial and ganglion cells, causing inflammation.

Otitis and sinusitis: frequent in children; produce tympanic membrane rupture in 50% of cases.

Whooping cough (pertussis): caused by Bordetella pertussis. Diagnosis: nasopharyngeal culture shows metallic-looking colonies. Treatment: erythromycin.

Lower Respiratory Tract

Acute bronchitis: inflammation of the bronchial and tracheal tree, caused by Streptococcus pneumoniae and Haemophilus influenzae.

Chronic bronchitis: predisposing factors include smoking, environment, etc. Causative agents include Streptococcus pneumoniae, Haemophilus, herpes simplex virus, and rhinovirus.

Pneumonia: alveoli filled with edematous fluid and an inflammatory reaction. Entry occurs via inhalation and oropharyngeal aspiration. Types: lobar, bronchopneumonia, atypical. Etiology: in community-acquired cases, Streptococcus pneumoniae and Haemophilus; in hospital-acquired cases, Staphylococcus aureus.

Pneumonia caused by Streptococcus pneumoniae: diagnosis by direct visualization; culture shows alpha-hemolytic, umbilicated colonies and mucosal involvement. Antibiogram recommended.

Legionellosis: transmitted by inhalation of aerosols from contaminated water. Diagnosis: PCR, antibody testing, X-ray. Treatment: penicillin.

Tuberculosis (TB): caused by Mycobacterium tuberculosis. Pathogenesis: inhaled aerosols, transmitted person to person. Diagnosis: Ziehl-Neelsen staining, Löwenstein culture, PCR, Mantoux test, X-ray. Treatment: isoniazid, pyrazinamide.

Genitourinary Tract Infections

Sexually transmitted and genitourinary infections:

Syphilis: an infectious disease transmitted through sexual contact or blood. Causative agent: Treponema pallidum. Diagnosis: microscopy.

Gonorrhea: caused by Neisseria gonorrhoeae. Reservoir: asymptomatic women; often coinfected with Chlamydia. Entry through the vagina, urethral mucosa, mouth, and rectum. Diagnosis: microscopy, culture, tests.

Chlamydia: infection transmitted sexually, caused by a small obligate intracellular bacterium.

Genital herpes: treatment with famciclovir. Two types: HSV-1 and HSV-2. Primary infection can be very severe: erythema followed by vesicles that break, leaving very painful ulcers, nodules, swollen lymph nodes, and fever.

Trichomoniasis: treatment with metronidazole; the parasite moves using four flagella.

Candidiasis: treatment with clotrimazole or miconazole. Candida is normal flora in the vagina; symptoms include white discharge and pruritus. Diagnosis: direct visualization.

Urinary tract infection (UTI): more frequent in women; etiology: E. coli. Two types: cystitis (dysuria, urgency, frequency, cloudy urine, suprapubic pain) and pyelonephritis (kidney involvement). Diagnosis: microscopy and culture. Treatment: fosfomycin.