Respiratory Tract Infections Flashcards
2 Lower tract bacterial infections
Pneumonia (community or hospital acquired)
Acute exacerbations of chronic bronchitis COPD
3 Upper tract infections
Sinusitis
Otitis media
Pharyngitis
Examples of RTI specimens
Sputum
BAL/bronchial washing (with bronchoscope)
Nasopharyngeal aspirates/swabs
Endotracheal aspirates
Sinus aspirates (have to punch through bone)
Tympanocentesis (needle through eardrum and aspirate)
Throat swabs
When grading sputum, what do you want to see?
HIGH numbers of neutrophils, LOW numbers of epithelial cells
3 common resp tract pathogens
Strep pneumoniae (vast majority)
Haemophilus influenzae
Moraxella catarrhalis
3 Atypical pathogens
Mycoplasma pneumoniae
Chlamydophyla pneumoniae
Legionella pneumonphila
Empirically you need to make sure to cover…
Strep pneumoniae
The atypical pathogens
Pneumonia
An inflammatory condition of the lung primarily affecting the alveoli
Severity of disease and mortality vary considerably
Community, hospital, or ventilator acquired
Typical signs and symptoms of pneumonia
Fever
Cough (productive or dry)
Chest pain
Shortness of breath
S. pneumoniae
Most common bacterial cause of RTIs
Small gram positive diplococci
Alpha hemolytic, bile soluble, optochin S***
Growth enhanced by CO2
Most are encapsulated
Colonizes the nasopharynx in 5-10% of adults and 20-40% of children (cannot take throat swabs)
Incidence increases in winter months
6 factors that cause a disposition to pneumococcal infection
- Defective Ab formation
- Insufficient numbers of PMNs
- Living in close quarters
- Chronic resp disease
- Infancy and aging
- Diabetes, alcoholism, liver disease
How do you diagnose otitis media?
Look in the ear and see it is red
HAVE to blow air through the otoscope and see how much the eardrum moves
Red ear does not mean otitis
S. pneumoniae virulence factors (3)
Capsule (most important - aids in adherence and escape from phagocytic cells)
Pneumolysin (hemolysin - destroys ciliated epithelial cells, activates complement, suppresses oxidative burst by phagocytic cells
Secretory IgA protease
2 vaccines for pneumonia
- Pneumococcal vaccine - Pneumovax (directed against 23 most common capsular serotypes that cause invasive disease (get into the blood) - but carbohydrate based so no lasting immunity, not very immunogenic, and doesnt work against kids)
- Prevnar (conjugate vaccine - to diptheria toxoid)
Drug treatment for S. pneumoniae
Penicillins (cannot use empirically though - too much resistance) Cephalosporins Macrolides Fluoroquinolones Vancomycin
COPD
Chronic obstructive pulmonary disease
An umbrella term used to describe progressive lung diseases (emphysema, chronic bronchitis, refractory asthma, some forms of bronchiectasis)
Characterized by increasing breathlessness
Haemophilus influenzae
Most common cause of AE-COPD Small gram negative bacilli Requires X and V factors Will grow on chocolate agar May be encapsulated Type B caused major invasive disease - epiglottitis Satelliting growth on SBA with S. aureus
Porphyrin Test
Determines and isolates X factor requirement
Heavy suspension in amino-levulinic acid, incubate 4 hours, illuminate with UV light and examine for red fluorescence
Positive = X factor independent
H. influenzae Treatment
Approx 18% produce beta lactamase and 1% have altered PBP
2nd/3rd gen cephalosporins
Newer macrolides ok
Fluoroquinolines good, but not in children
Amoxicillin-clavulanate very effective
Which two drugs can you NOT use to treat H. influenzae?
Septra
Penicillin
Moraxella catarrhalis
size, gram stain, shape, associated with what diseases, carriage rate, resistant to, susceptible to
Small gram negative cocco-bacilli
Associated with otitis media, sinusitis, AECB
Carriage rate about 50%
DNase+, asacchrolytic
90% strains resistant to amp/amoxi and Septra
Susceptible to most oral antibiotics
Legionella pneumophila (gram stain, shape, intra/extracellular, where is it found in environment, illness, media, staining, requires what for growth)
Gram negative bacilli Intracellular pathogen Widespread in environment (soil, water, taps, showers) Widespread spectrum of illness Requires special media to grow - BCYE agar Faintly stains, easy to miss Asaccharolytic Requires L-cysteine for growth! Stimulated by 5% CO2
Why do you have to put charcoal or blood in the media with Legionella?
Because you need them to mop up the toxins so they will grow!
2 ways to get a Legionella diagnosis in the lab?
Urinary antigen test
Culture
NOT DFA testing or serology
2 drugs used to treat Legionella
Fluoroquinolones
Macrolides
Mycoplasma morphology and physiology
Lack a cell wall!! Smallest free living bacteria Small genome Require complex media to grow Facultative anaerobes except M pneumonia (strict aerobe)
2 diseases M. pneumoniae causes
- Tracheobronchitis (70-80% of infections, post infectious cough)
- Pneumonia (20-30% of infections, mild disease but long duration, most common cause of atypical pneumonia)
3 drugs the atypicals are susceptible to (myco and chlamydophyla)
- Doxycycline
- Macrolides
- Fluoroquinolones
Not susceptible to cell wall active agents
Bordetella pertussis
Causes pertussis Small gram negative cocci-bacilli Strictly aerobic, fastidious Requires growth on media containing charcoal, blood or starch BG or RL media
3 stages of pertussis
- Catarrhal stage (1-2 weeks, non specific upper tract infection - sneezing, runny nose mild cough, low grade fever, very contagious)
- Paroxysmal stage (1-6 weeks, paroxysmal cough, inspiratory whoops, vomitting, cyanosis, exhaustion, leukocytosis, lymphocytosis)
- Convalescent stage (2-3 weeks, gradually resolves, may return if patients acquire secondary infection)
Incubation period of pertussis
7-10 days
Range 4-21
Specimen and drug for pertussis
Naso-pharyngeal specimens
Treat with Macrolides
Strep pyogenes
Gram positive, catalase positive, beta-haemolytic, group A, PYR +, Taxo A (bacitracin) S
Complications: rheumatic heart disease, post-streptococcal glomerulonephritis
2 drugs to treat S pyogenes
Penicillin
Amoxicillin
2 reasons to treat bacterial pharyngitis
- Eradication
2. Prevents complications (antibodies can prevent or minimize risks, wait for culture results)
2 main ways viral RTIs are transmitted
Droplet (not aerosol)
Contact (inoculate nose/eyes)
Factors contributing to severity of viral diseases (4)
Inoculum size
Virulence traits
Immune system (compromised or not)
Co-morbidities
Most common virus causing RTIs
Rhinovirus
Coronavirus is second
2 ways to collect viral specimens
Nasopharyngeal swab or aspirates for URTIs (swab has to be transported in a special media, use flocked swab, throat swab isn’t as good as NP swabs)
Bronchial alveolar lavages for LRTIs (transport in sterile container)
Best way to detect respiratory viruses
Molecular methods (high sensitivity and specificity! Can use qualitative real-time multiplex RT-PCR for FluA/B/RSV)
Rhinovirus
family, nucleic acid/sense, enveloped or not, diseases
Picronaviridae family ssRNA (+) Non-enveloped >100 serotypes (no vaccine) Most common viral RTI
Coronavirus
family, nucleic acid/sense, enveloped or not, diseases
Coronaviridae family ssRNA (+) Enveloped Cause of common cold (second to rhino) Some have caused more severe disease (SARS)
Enterovirus
family, nucleic acid/sense, enveloped or not, diseases
Picronaviridae family ssRNA (+) Non-enveloped 12 species, over 100 serotypes Affect millions worldwide each year Usually mild respiratory illness Certain ones have been linked to polio like illnesses with paralysis (EV - D68)
Respiratory syncytial virus
family, nucleic acid/sense, enveloped or not, diseases
Paramyxoviridae family
ssRNA (-)
Enveloped
RSV A and RSV B
Most common cause of bronchiolitis in children
Spreads rapidly in households and daycares
Can affect adults (do not have lasting immunity)
Severe infections may be fatal (co-morbidities: heart and lung disease, treat with passive immunization palivizumab)
3 groups of people most at risk for respiratory disease
Children
Elderly
Immunocompromised
Parainfluenza viruses
family, nucleic acid, enveloped?, causes
Paramyxoviridae family ssRNA (-) Enveloped 4 types Common cause of URTIs in children 2% get croup (laryngotracheobronchitis - barking cough - inflammation of upper airways and narrowing of subglotic region)
Adenovirus
genome, enveloped?, causes, types
dsDNA Non-enveloped Over 60 types have been identified URTIs or LRTIs Types 40 and 41 are GI viruses (cause diarrhea)
Influenza
family, nucleic acid, enveloped?, types
Orthomyxoviridae
ssRNA (-)
Enveloped
Segmented genome
3 types (A, B, C)
FluA and B cause seasonal epidemics each year
FluA is most important (pandemic potential, more severe disease)
Subtyping based on hemagglutinin and neuraminidase
Common symptoms for influenza
Cough Fever Malaise Fatigue, weakness Severe muscle pain
2 classes of antiviral treatment for influenza
Amantidine (M2 inhibitor) Neuraminidase inhibitors (oseltamivir and zanamivir)
Function of:
Hemagluttinin
Neuraminidase
Hemagluttinin: binds to sialic acid to allow viral entry to the cell
Neuraminidase: cleaves the HA binding to sialic acid to release viral particle
Amantidine Resistance
Mutations in amino acids in the M2 channels
All H3N2 human strains are resistant
Doesn’t work against influenza B (no M2 channels)
No longer used
Neuraminidase inhibitors
Mutations in NA or HA
Most circulating strains are susceptible
Influenza vaccine
Trivalent or quadravalent vaccine
Needs to be updated every year
Protection good when matched to circulating viruses, but antigenic drift occurs
Antigenic drift
Due to mutation over time in surface glycoproteins (HA and NA)
Occurs in both FluA and B
May lead to a vaccine mismatch or lack of immunity
Antigenic shift
Genetic reassortments between avian/swine/human
Only occurs in FluA
Emergence of pandemics
No pre-existing immunity
Influenza
- Natural reservoir
- Mixing vessel
- Aquatic birds
2. Pigs
Avian Influenza A (H5N1)
Transmission by direct contact with infected poultry or objects contaminated by their feces
Exposure is most likely during slaughter and cooking prep
Doesn’t usually spread person to person very readily - not adapted to humans
H1N1 versus H5N1
H1N1: Easily spread, rarely fatal
H5N1: Spreads slowly, often fatal
Arcanobacterium hemolyticum
causes what with what symptoms, hemolytic, treat with, grows best with
Causes pharyngitis in teen and young adults (16-24)
Rash (like scarlet fever), RHD or AGN
Invasive disease occurs, but rare
May respond poorly to penicillin, but disease is self limiting
Grows best in CO2 for 48 hours
Weakly beta hemolytic (best on rabbit blood)
Anaerobically: slower growth
Penicillin + gentamicin or clindamycin used
Factors (out of X, V, and Catalase) needed for H influenzae, H parainfluenzae, and Aggregatibacter aphrophilus
H influenzae: X, V, and catalase +
H parainfluenzae: V +, catalase +/-
A. aphrophilus: negative for all
