Respiratory System Infections

The respiratory system is divided into 2 parts:

1.) Upper respiratory tract

2.) Lower respiratory tract

Upper respiratory tract is composed of:

• mouth

• nose

• nasal cavity

• sinuses

• throat or pharynx

• larynx

Lower respiratory tract is composed of:

• trachea

• bronchi

• bronchioles

• alveoli

The first line of defense:

• nasal hair traps particles

• cilia propel particles upward and out of the respiratory tract

• mucus is a natural trap for invading microorganisms

The second and third lines of defense:

• complement

• antimicrobial peptides

• cytokines

• macrophages

• secretory IgA

Respiratory Tract Normal Biota:

• healthy upper respiratory system harbors thousands of commensal microorganisms

• even lungs have a limited, normal biota

• most normal biota CAN cause serious disease

Upper respiratory tract normal biota:

many species of bacteria and fungi, including Neisseria meningitidis, Staphylococcus, Streptococcus, Aspergillus, and other fungi

Lower respiratory tract normal biota:

still unclear; low levels of colonization by multiple species probable

T/F The composition of the lung microbiome differs in patients who are smokers or who have COPD, asthma, and cystic fibrosis

True

Normal biota performs the function of microbial antagonism:

• reduces the chances of pathogens establishing themselves by competing for resources and space

  • ex. Lactobacillus sakei suppresses Corynebacterium tuberculostearicum in the sinuses

Pharyngitis — signs and symptoms:

• pain

• inflammation of the throat

• red and/or swollen mucosa

Pharyngitis: sore throats caused by ______ are more painful than those caused by _____, and more likely to be accompanied by fever, headache, and nausea

bacteria; viruses

Pharyngitis — causative agents:

• the same viruses causing the common cold

• result of mechanical irritation from prolonged shouting or drainage from the sinus cavity

• most serious cases of pharyngitis caused by Streptococcus pyogenes, a group A streptococcus (GAS)

Pharyngitis: Streptococcus pyogenes

• Gram-positive coccus that grows in chains

• does not form endospores

• nonmotile

• forms capsules and slime layers

• facultative anaerobe that ferments a variety of sugars

• does not produce catalase

• peroxidase system allows for its survival in the presence of oxygen

Pharyngitis: Streptococcus pyogenes — virulence factors:

virulence is a result of two phenomena

• ability of surface antigens to mimic host proteins

• possession of superantigens

• specialized polysaccharides protect the bacterium from being dissolved by lysozyme

• lipoteichoic acid: contributes to the adherence of the cell wall to the epithelial cells of the pharynx

• M protein: resists phagocytosis, contributes to adherence

• Hyaluronic acid capsule: contributes to adhesiveness

Pharyngitis: Streptococcus pyogenes — 2 extracellular toxins:

1.) Streptolysins

2.) Erythrogenic toxin

Pharyngitis: Streptococcus pyogenes — Streptolysins (O and S)

• cause beta-hemolysis of sheep blood agar

• rapidly injure cells and tissues

Pharyngitis: Streptococcus pyogenes — Erythrogenic toxin

• responsible for the bright red rash

• induces fever

• only lysogenic strains of S. pyogenes that contain genes from a temperate bacteriophage can synthesize this toxin

Pharyngitis: Streptococcus pyogenes — transmission and epidemiology:

• 30% of sore throats may be caused by S. pyogenes

• transmission via respiratory droplets or direct contact with mucus secretions and fomites

• humans are the only significant reservoir

• more than 80 serotypes of S. pyogenes exist; immunity is serotype specific

Pharyngitis: Streptococcus pyogenes — culture and diagnosis:

Rapid diagnostic tests of pharyngeal swab specimens:

• use antibodies to detect GAS

Culturing of pharyngeal swab specimens:

• plated on sheep blood agar

• S. pyogenes casues beta-hemolysis

• distinguish from beta-hemolytic group B streptococci and enterococci

• Bacitracin disc test

Pharyngitis: Streptococcus pyogenes — prevention:

• no vaccine exists

• prevention through good hand washing

Pharyngitis: Streptococcus pyogenes — treatment:

• Penicillin is the antibiotic of choice

• Cephalexin used for patients with penicillin allergy

• most sore throats caused by S. pyogenes can resolve on their own, but antibiotic treatment is needed to prevent serious sequelae

Pharyngitis: Streptococcus pyogenes — Sequelae

• Scarlet fever

• Rheumatic fever/rheumatic heart disease

Scarlet fever

• result of an infection of S. pyogenes infected with a bacteriophage

  • produces erythrogenic toxin

  • sandpaper-like rash with high fever

  • fatality rate up to 95%

Rheumatic fever/rheumatic heart disease

• due to an immunologic cross-reaction between streptococcal M proteins and the proteins in joints, the heart, etc.

The Common Cold — causative agent:

→ over 200 different viruses

• Rhinoviruses: 150 serotypes

• Coronavirus

• Adenovirus

• Respiratory syncytial virus

The Common Cold — transmission:

• indirect contact, droplet contact

The Common Cold — symptoms:

• sneezing

• scratching throat

• runny nose

• fever in children

Sinusitis — causative agents:

• various viruses

• various bacteria

• various fungi (less common)

• allergies and structural abnormalities are common noninfectious causes

Sinusitis — treatment:

• broad-spectrum antibiotics for bacterial infection

• antifungals and/or surgery for fungal infection

Acute Otitis Media (Ear infection)

• viral infections of the upper respiratory tract lead to inflammation of Eustachian tubes, buildup of fluid in the middle ear, and bacterial multiplication in the fluid

Acute Otitis Media (Ear infection) — causative agents:

• Streptococcus pneumoniae

• Candida auris

• Other bacteria/viruses

Ear infection — prevention:

Prevnar

Ear infection — treatment:

• “watchful waiting”

• Antibiotics

• Tympanic membrane tubes

Pneumonia is a disease characterized by an _______ diagnosis. Why?

Anatomical; Pneumonia is defined as an inflammatory condition of the lung in which fluid fills the alveoli

Pneumonia statistics:

Can be deadly, and across the globe, more children under the age of 5 die from pneumonia than any other infectious disease

Pneumonia — causative agents:

• bacteria, fungi, and a wide variety of viruses can cause pneumonias

  • Have appropriate characteristics that allow them to penetrate and survive in the lower respiratory tract

  • Avoid phagocytosis or avoid being killed once inside macrophage

Community-acquired pneumonias

• Streptococcus pneumoniae

• Legionella

• Mycoplasma pneumoniae and Chlamydophila pneumoniae

• Histoplasma capsulatum

• Hantavirus

• Secondary effect of influenza

Streptococcus pneumoniae (CAP)

• factors that favor the ability of the pneumococcus to cause disease are old age, the season underlying viral respiratory disease, diabetes, and chronic abuse of alcohol or narcotics

Legionella (CAP):

• less common

• Serious cause of disease

Mycoplasma pneumoniae and Chlamydophila pneumoniae:

Walking pneumoniae

Histoplasma capsulatum (CAP):

• fungus that infects many people but causes a pneumonia-like disease in relatively few

Pneumonia can be a _______ effect of influenza

Secondary

SARS-CoV-2

• coronavirus

• It is an RNA virus with spikes (glycoproteins) which allow it to attach to host cells

How did coronavirus get its name?

Glycoprotein spikes are visible under the electron microscope and give it its name corona, for crown

What does Corona mean?

Crown

SARS-CoV-2 was recognized as causing a _____ pneumonia

Deadly

SARS-CoV-2 facts:

• on December 31, 2019, a cluster of pneumonia cases of unknown etiology was reported in Wuhan, China

• By January 9, 2020, the Chinese CDC identified the cause as a novel coronavirus, which was later officially named SARS-CoV-2

• The disease it causes is called COVID-19

SARS-CoV-2 — signs and symptoms:

• COVID-19 may cause no symptoms at all, or it may lead to death quickly

• It can damage blood vessels all over the body, leading to damage to the heart, kidneys, brain, and other organs

• Patients report post-COVID symptoms that reflect the systemic nature of this virus, lasting for weeks to months

• Children and young adults also are at risk for a condition called MIS-C (multi-system inflammatory syndrome in children)

SARS-CoV-2 — pathogenesis:

• it triggers widespread activation of bradykinins, which cause damage to lungs and other tissues

  • Bradykinin storm

• Early studies suggest that the virus has proteins that block the production of interferon, crippling an important part of the innate immune response

SARS-CoV-2 — epidemiology:

• transmitted through droplet and airborne contact

• One factor making the pandemic difficult to control is that it is transmissible even in the absence of symptoms, so “well” people circulating between public spaces and home are reservoirs and carriers

SARS-CoV-2 — culture and diagnosis:

• scientists acted quickly and grew the virus in cell culture

• Testing for the virus was not terribly successful in the beginning

SARS-CoV-2 — prevention and treatment:

• vaccine development started immediately and initial vaccines were available within months

• The best preventions in lieu of a vaccine are physical distancing and the use of face masks

Streptococcus pneumoniae (CAP) facts:

• Pneumococcus

• small, gram-positive flattened coccus, often appearing in pairs lined up end to end

• vaccination with PPSV23 or PCV13 encouraged in older adults

Risk facts for Streptococcus pneumoniae:

• old age

• the season

• underlying viral respiratory disease

• diabetes

• chronic abuse of alcohol or narcotics

Legionella pneumophila (CAP) facts:

• weakly gram-negative bacterium that ranges from coccus to filaments

• able to survive and persist in natural habitats

• widely distributed in tap water, cooling towers, spas, ponds, and other fresh water

  • resistant to chlorine

  • can live in association with free-living amoebas

• released during aerosol formation and carried long distances

What are 2 atypical pneumonias (CAP)?

Mycoplasma and Chlamydophila

What does atypical pneumonia mean?

→ symptoms do not resemble those of pneumococal or other severe pneumonias

Mycoplasma and Chlamydophila (CAP) facts:

• transmitted by aerosol droplets among people in confined to close living quarters

• family, students, the military

• “walking pneumonia”

  • lack of acute illness in most patients

What does “walking pneumonia” mean?

lack of acute illness in most patients

Hantavirus (CAP) facts:

• 1993: cluster of unusual cases of severe lung edema among healthy young adults in the Four Corners area

• Bunyaviridae family: enveloped virus

• associated with the presence of mice in close proximity with humans:

  • transmitted via airborne dust contaminated with urine, feces, or saliva of infected rodents

• localized outbreak in 2012 in Yosemite

Histoplasma capsulatum (CAP) facts:

• endemically distributed in all continents except Australia

• highest incidence in eastern and central US

• grows most abundantly in moist soils high in nitrogen content, especially those supplemented with bird and bat droppings

• distribution determined by injecting fungal extract into the skin and monitoring for allergic reactions (much like the TB skin test)

Pneumocystitis (carinii) jiroveci (CAP) facts:

• discovered in 1909

• agent of pneumocystitis pneumonia

• one of the most frequent opportunistic infections in AIDS patients

• likely transmitted through the inhalation of spores

• traditional antifungal drugs are ineffective against Pneumocystis pneumonia because of the chemical makeup of the organism’s cell wall

Respiratory viruses (CAP) facts:

• very common causes of community-acquired pneumonia

• either residents of the upper respiratory tract or acquired through daily activities

• viral pneumonias are generally mild

Healthcare-associated pneumonia (HAP):

• up to 1% of hospitalized or institutionalized people experience pneumonia

• it is most commonly associated with mechanical ventilation, via an endotracheal or tracheostomy tube

  • this is sometimes labeled “ventilator-associated pneumonia,” or VAP

• mortality rate: 30-50%

What is meant by “ventilator-associated pneumonia” or VAP?

most commonly associated with mechanical ventilation, via an endotracheal or tracheostomy tube

HAP — most frequent causes:

• MRSA strains of Staphylococcus aureus

• gram-negative bacteria: Klebsiella pneumoniae, Enterobacter, E. coli, Pseudomonas aeruginosa, and Acinetobacter

• many are polymicrobial in origin

HAP — culture and diagnosis:

• sputum and tracheal swabs are NOT useful

• endotracheal tube or bronchoalveolar lavage cultures provide better information but are invasive

• antibiotics the patient is already receiving may affect results

HAP — prevention and treatment:

• elevation of patients’ heads to a 30- to 45-degree angle helps reduce aspiration of secretions

• good preoperative education of patients about the importance of deep breathing; and frequent coughing can reduce postoperative infection rates

• proper care of mechanical ventilators and respiratory therapy equipment

• empiric therapy should begin as soon as hospital-associated pneumonia is suspected

Influenza