Comprehensive Respiratory and Infectious Disease Review for Medical Students

What are the structural differences between the upper and lower respiratory tracts? How do these differences relate to their susceptibility to infection?

The upper tract includes the nose, nasal cavity, sinuses, pharynx, epiglottis, larynx, while the lower tract includes the trachea, bronchi, bronchioles, and alveoli. The upper tract is more exposed, so it gets infections more easily, while the lower tract is normally nearly sterile because it has stronger defenses.

What is the function of the hairs (cilia and vibrissae) in the nasal passages?

They trap particles and help move mucus and trapped microbes out of the airways.

The lower respiratory tract is normally nearly sterile. What is the primary mechanism responsible for maintaining this sterility?

The ciliary escalator, mucus, and macrophages help keep it sterile, with cilia moving trapped material upward.

How would you define each of the following, and what structure or region of the respiratory tract does each affect: pharyngitis, rhinitis, tonsillitis, sinusitis, and otitis media?

Pharyngitis = inflammation of the throat; rhinitis = inflammation of the nasal cavity; tonsillitis = inflammation of the tonsils; sinusitis = inflammation of the sinuses; otitis media = inflammation of the middle ear.

Streptococcal pharyngitis

Caused by Streptococcus pyogenes; it causes a sore, red, swollen throat, swollen tonsils, and sometimes foul breath or white patches. It can be prevented with good hygiene and treated with antibiotics.

Scarlet fever

Caused by Streptococcus pyogenes with erythrogenic toxin; it causes strep throat plus a sandpaper-like rash and high fever. Prevention is the same as strep throat, and treatment is antibiotics.

Diphtheria. Additionally, how does the bacterium acquire the toxin gene, and what vaccine is used for prevention?

Caused by Corynebacterium diphtheriae. It acquires the toxin gene from a bacteriophage, and it is prevented by the diphtheria toxoid vaccine in DTaP.

Rheumatic fever. Also, what is its relationship to streptococcal infection?

It is an immune complication that can occur about 3 weeks after Streptococcus pyogenes pharyngitis. It can damage the heart and joints.

Otitis media

It is a middle-ear infection, usually caused by a mixed infection of viruses and bacteria such as Streptococcus pneumoniae and Haemophilus influenzae.

What types of viruses are responsible for the common cold? Why is there no single vaccine for this disease?

More than 200 viruses can cause it, including rhinoviruses, coronaviruses, adenoviruses, and RSV. There is no single vaccine because there are so many different causes.

Pertussis (Whooping Cough) What is the causative agent of pertussis, and what are its characteristic symptoms?

It is caused by Bordetella pertussis. It causes severe coughing fits and the "whooping" sound.

The "whooping" sound is a defining clinical feature. Which specific cells does the pathogen attack to produce this symptom?

It attacks ciliated cells in the respiratory tract.

What vaccine provides protection against pertussis?

DTaP.

What special staining characteristic does Mycobacterium tuberculosis have, and why is this significant?

It is acid-fast positive because of its waxy mycolic acid outer layer. This helps identify it in the lab.

What does a positive tuberculin skin test (PPD) indicate? Does it distinguish between latent and active infection?

It indicates exposure to TB, not necessarily active disease. It does not distinguish latent from active infection.

What is latent TB, and how does it differ from active disease?

Latent TB has no symptoms and is not contagious, but the bacteria remain in the body. Active TB causes symptoms and is contagious.

Can you trace the specific stages of TB pathogenesis, from initial macrophage ingestion through tubercle formation, caseous necrosis, liquefaction, and cavity formation?

Yes: 1) inhaled bacteria are ingested by alveolar macrophages, 2) early tubercle forms, 3) caseous center forms, 4) liquefaction occurs, 5) a tuberculous cavity forms.

What are the major bacterial causes of pneumonia covered in this lesson? For each, what is the causative agent, which population is most at risk, and what are distinguishing features?

Streptococcus pneumoniae causes typical pneumonia with high fever and rust-colored sputum, often in older adults; Mycoplasma pneumoniae causes walking pneumonia, usually mild, in children and young adults; Legionella pneumophila is linked to older men who drink or smoke heavily and is found in water systems.

Which group of bacterial pathogens causes "walking pneumonia," and what is the causative organism's name?

It is caused by Mycoplasma pneumoniae, an atypical pneumonia pathogen.

Why is Mycoplasma pneumoniae resistant to penicillin? What structural characteristic makes this organism unique among bacteria?

It is resistant because it has no cell wall. It is unique because it is wall-less and pleomorphic.

Where is Legionella pneumophila typically found in the environment, and how does this explain its pattern of transmission?

It lives in water collection sites such as air-conditioning systems and cooling towers, and spreads when contaminated droplets become airborne.

Viral pneumonia: what viruses can cause it?

Different viruses can cause viral pneumonia, including influenza and other respiratory viruses.

Influenza: what are hemagglutinin (H) and neuraminidase (N), and what is the specific function of each surface protein in the infection process?

Hemagglutinin helps the virus attach to and enter host cells, and neuraminidase helps release new virus particles from the host cell.

COVID-19: what specific unusual symptoms distinguish it from other respiratory infections? What is the name of the causative virus? What types of vaccines have been developed, specifically comparing mRNA and viral vector approaches?

COVID-19 can cause loss of taste or smell, GI symptoms, skin rashes, and "COVID toe" or "COVID tongue." It is caused by SARS-CoV-2. The vaccines listed are mRNA vaccines (Pfizer-BioNTech and Moderna) and a viral vector vaccine (Johnson & Johnson/Janssen).

RSV: which specific age group is most commonly and most severely affected?

Children under 1 year of age are most commonly and severely affected.

Histoplasmosis: what is the specific environmental source?

It comes from dry, dusty soil, chicken coops, and bat caves.

Coccidioidomycosis: what is the specific environmental source?

It is acquired by inhaling spores from soil.

Cryptococcosis: which population is at greatest risk?

Immunocompromised people are at greatest risk.

Pneumocystis Pneumonia (PCP): which specific population is at greatest risk, and why?

AIDS patients are at greatest risk because the infection is opportunistic and occurs when immune defenses are weak.

What is the primary bacterium responsible for dental caries?

Streptococcus mutans.

What three factors must be present simultaneously for caries to develop (the "caries triangle")?

Plaque, dietary carbohydrates, and acidogenic bacteria.

What metabolic process do cariogenic bacteria use to damage tooth enamel?

They ferment carbohydrates into acids that damage enamel.

Can you trace the progressive stages of tooth decay, from initial enamel demineralization all the way to pulp involvement?

The tooth starts with enamel demineralization, then decay progresses deeper through the tooth layers until the pulp is involved.

How does poor oral hygiene and subgingival plaque accumulation contribute to the development of periodontal disease?

Poor oral hygiene lets plaque build up below the gums, which allows bacteria to cause inflammation and tissue damage.

What is the progression from gingivitis to periodontitis? What specific tissues are damaged at each stage?

Gingivitis causes inflammation and bleeding at the gingival margin. Periodontitis damages the periodontal ligaments and alveolar bone, which can loosen teeth.

What is the final outcome if periodontal disease is left untreated?

Teeth can become loose or be lost.

Staphylococcal food poisoning

Caused by Staphylococcus aureus in contaminated meats, dairy products, or pastries. It causes nausea, vomiting, and diarrhea, and treatment is usually supportive because it is an intoxication.

What is the causative agent of Shigellosis (bacillary dysentery), how does it spread, symptoms, treatment

Caused by Shigella spp., spread by fecal-oral contamination. It causes bloody diarrhea, tissue damage, and fever, and is treated with quinolones antibiotics.

Salmonellosis

Caused by Salmonella enterica. It causes nausea and diarrhea and is usually treated with oral rehydration.

Typhoid fever

Caused by Salmonella typhi. It causes high fever and serious illness, and treatment includes quinolones or cephalosporins.

Cholera

Caused by Vibrio cholerae. It causes massive watery fluid loss, usually from contaminated water or raw shellfish, and treatment is oral rehydration.

E. coli gastroenteritis — how do traveler's diarrhea (ETEC) and Shiga toxin-producing E. coli (STEC) differ from each other?

ETEC causes watery traveler's diarrhea, while STEC causes bloody diarrhea and can lead to kidney damage and hemolytic uremic syndrome.

Peptic ulcer disease

Helicobacter pylori can cause gastric ulcers. It survives stomach acid by making urease, which produces ammonia and neutralizes acid.

How does the incubation period differ between intoxications and infections? Why do symptoms appear more quickly in intoxications?

Infections usually take 12 hours to 2 weeks, while intoxications cause symptoms in 1 to 48 hours. Symptoms appear faster in intoxications because the toxin is already present in the food.

o Staphylococcal food poisoning

o Shigellosis (bacillary dysentery)

o Salmonellosis

o Typhoid fever

o Cholera

o E. coli gastroenteritis

o Peptic ulcer disease

Which of the diseases listed above involve actual invasion of epithelial cells?

Shigellosis and some E. coli infections, especially ETEC and STEC, involve infection of intestinal cells.

Which disease can result in chronic carriers after recovery, and approximately what percentage of recovered patients become carriers?

Typhoid fever can produce chronic carriers, and about 13% of recovered patients become carriers.

How does Helicobacter pylori survive in the highly acidic environment of the stomach?

It makes urease, which produces ammonia and neutralizes stomach acid.

What type of virus causes mumps, and how is it transmitted?

Mumps is a viral infection spread person to person through infected saliva.

What is the primary site of infection, and why does this classify mumps as a digestive system disease even though it is spread through the respiratory route?

It infects the parotid salivary glands, which are part of the digestive system.

What is the characteristic symptom that distinguishes mumps from other viral infections, and what is the alternative medical name for this condition?

Swollen salivary glands causing enlarged jaw tissues; the other name is infectious parotitis.

What are the two most common causative viruses of viral gastroenteritis?

Rotavirus and norovirus.

How do the duration of symptoms and incubation period compare between rotavirus and norovirus?

Rotavirus usually incubates for 1 to 3 days and lasts about 1 week; norovirus incubates for 24 to 48 hours and is usually shorter.

What are the typical symptoms of Viral Gastroenteritis, and what is the standard treatment approach?

Typical symptoms are vomiting and diarrhea, and treatment is oral rehydration.

Why are these infections considered self-limiting? (Viral Gastroenteritis)

They usually go away on their own with supportive care.

Giardia lamblia: what are the two morphological forms, and which form is responsible for transmission and why?

The two forms are trophozoite and cyst. The cyst is mainly responsible for transmission because it survives better in the environment.

How long can cysts survive in the environment, and what is the infectious dose?

Cysts can survive about 2 months, and the infectious dose is 10 to 100 cysts.

What is the route of transmission, and what are the characteristic symptoms?

It is spread by swallowing cysts in contaminated food or water. Symptoms include long-lasting diarrhea, abdominal pain, flatulence, and greasy, foul-smelling stool.

Why is fever typically absent in giardiasis?

Because it mainly causes intestinal irritation without strong tissue invasion.

What prevention strategies are most effective? (Giardia lamblia)

Avoid drinking from freshwater sources and prevent contamination of food and water.

What are the life cycle stages of Entamoeba histolytica?

It alternates between a trophozoite and a cyst.

What is the mechanism of tissue invasion, including the role of enzyme production?

The trophozoites burrow into the intestinal wall and produce enzymes that dissolve tissue.

What are the characteristic symptoms and complications?

It can cause mild diarrhea and stomach pain, or severe amebic dysentery with bloody stools and fever. It can also spread to the liver and sometimes the lungs or brain.

How does this infection differ from giardiasis in terms of tissue damage?

Entamoeba histolytica invades and destroys tissue, while Giardia mainly causes malabsorption and diarrhea without major tissue destruction.

What is the general distinction between nematodes (roundworms) and cestodes (tapeworms)?

Nematodes are roundworms, while cestodes are tapeworms that are segmented.

Hookworms: how do larvae enter the body, and how do they migrate?

Larvae enter through the skin, usually from contaminated soil, then travel to the lungs and are swallowed.

Pinworms (Enterobius vermicularis): what is the primary symptom and the route of transmission?

The main symptom is itching, and they spread by fecal-oral transmission.

Tapeworms (Taenia solium): how do humans become infected, and what are the primary symptoms?

Humans become infected by eating raw or undercooked pork. Symptoms include abdominal pain, weight loss, and passing tapeworm segments.

Trichinella spiralis (Trichinosis): what is the source of infection, and why does it affect multiple organ systems?

It comes from raw or undercooked meat. It affects multiple organ systems because larvae migrate through the body and encyst in muscle.

Ergot Poisoning: what is the causative fungus, what food source does it contaminate, and what are the primary vascular symptoms? What is its alleged historical significance?

It is caused by Claviceps purpurea, which contaminates grain. It reduces blood flow to the limbs and is historically linked to the "ergot" poison of grain.

Aflatoxin Poisoning — what is the causative fungus, what foods are commonly contaminated, what are the long-term health effects, and why is prevention the primary control strategy?

It is caused by Aspergillus flavus, often in food contaminated by mycotoxin. It can cause liver cirrhosis and liver cancer, and prevention is the main control because there is no treatment.

Compare and contrast intoxications and infections in bacterial GI diseases. Define each term, give examples of each, and describe how incubation period and fever presence differ between them.

An intoxication is illness from a preformed toxin, such as staphylococcal food poisoning or Bacillus cereus vomiting type; an infection is growth of the pathogen in the body, such as shigellosis or salmonellosis. Intoxications act faster and usually do not cause fever, while infections have longer incubation and may cause fever.

What are the main ways food and water become contaminated with GI pathogens? Consider contamination during food production, cross-contamination, water sources, fecal-oral transmission, and improper food storage.

Food can be contaminated during slaughter, by contaminated water used on fruits and vegetables, by infected food handlers, by cross-contamination with utensils, by sewage or fecal contamination of water, and by improper storage at unsafe temperatures.

What are the four main antimicrobial defenses found in urine itself?

Acidic pH, lysozyme, lactoferrin, and secretory IgA.

How does the flushing action of urination protect the urinary tract from infection?

It washes microbes out and helps shed infected epithelial cells.

Why are females more predisposed to urinary tract infections than males?

Females have a shorter urethra and the urethral opening is closer to the anus.

What is the most common source of microbial threat to the urinary tract?

Normal biota from the body, especially the GI tract.

What are the three main modes of transmission for reproductive system infections?

Direct sexual contact, blood-borne/parenteral transmission, and vertical transmission from mother to baby.

For each of the following, what is the primary mode of transmission: cystitis, pyelonephritis, gonorrhea, chlamydia, leptospirosis, and trichomoniasis?

Cystitis and pyelonephritis usually come from endogenous spread from the GI tract; gonorrhea, chlamydia, and trichomoniasis are mainly sexually transmitted; leptospirosis comes from contact with urine-contaminated water or soil.

What are the three main causative agents of cystitis? (Remember ESSP)

E. coli, Staphylococcus saprophyticus, and Proteus mirabilis.

What bacterial count in a urine culture is used as the threshold to diagnose a urinary tract infection?

About 10,000 bacteria per mL, or 100 coliforms per mL.

What are the key symptoms of cystitis, and what predisposing factors increase a person's risk?

Symptoms include frequent urination, burning pain, cloudy urine, blood in the urine, and low-grade fever or nausea. Risk is increased by poor hygiene and conditions that let gut bacteria enter the urinary tract.

What is pyelonephritis, and how does it typically develop in relation to cystitis?

It is an infection of one or both kidneys and often develops when a bladder infection spreads upward.

What is the most common causative agent?

Escherichia coli.

What symptoms distinguish pyelonephritis from cystitis?

Pyelonephritis causes high fever and back or flank pain.

How is it diagnosed and treated?

It is diagnosed by urine culture and a leukocyte esterase test, and treated with cephalosporins.

What is the causative agent of leptospirosis, and what animal reservoirs are involved?

It is caused by Leptospira interrogans, with dogs and rats as reservoirs.

How is it transmitted to humans, and what are the symptoms?

It spreads through contact with urine-contaminated water or soil and causes headache, muscle aches, fever, and sometimes kidney failure.

What are the diagnostic and treatment approaches? (Leptospirosis)

It is diagnosed with serological testing and treated with doxycycline or amoxicillin.

What is the causative agent of Gonorrhea, and what does its Gram stain result look like?

Gonorrhea is caused by Neisseria gonorrhoeae, a gram-negative coccus.

How do symptoms differ between males and females?

Males usually have painful urination and pus-like discharge; females often have few or mild symptoms and may mistake it for a bladder or vaginal infection.

What serious complication can develop in women if gonorrhea goes untreated?

Pelvic inflammatory disease can develop.

What are three systemic complications of untreated gonorrhea?

Endocarditis, meningitis, and arthritis.

What is ophthalmia neonatorum, and how is it prevented?

It is a serious eye infection in newborns caused by exposure during birth, and it is prevented by treating or screening the mother and using newborn eye prevention.

What are the diagnostic methods and treatment?

Diagnosis can use Gram stain, ELISA, or PCR, and treatment is fluoroquinolones.

What is the causative agent, and approximately what percentage of infected individuals are asymptomatic? (Chlamydia)

Chlamydia is caused by Chlamydia trachomatis, and about 75% to 90% of infected people are asymptomatic.

Why is chlamydia considered epidemiologically significant in the United States?

It is the most commonly reported notifiable disease in the United States.

Why is chlamydia harder to diagnose than gonorrhea?

Because many cases have no symptoms and it is an obligate intracellular infection, so it often needs special tests like PCR or ELISA.

What neonatal complications can occur from untreated maternal infection?

Eye infections, blindness, and pneumonia.

What does PID involve anatomically?

It is infection of the female reproductive tract, especially the uterine tubes.

What are the two most common causative agents?

Neisseria gonorrhoeae and Chlamydia trachomatis.