Opportunistic Infections (Buxton) Flashcards
What are 3 things that can compromise a host?
Defects/injury to physical barriers
Deficiencies in innate immunity
Deficiencies in adaptive immunity
A 12 year old child is severely burned in a house fire. He was hospitalized for over a month with 3rd degree burns on his leg. About a week after admission, he developed an infection of the burned areas. Blue-green pus was associated with the infection.
What factors increased this child’s risk of infection?
Burn - loss of protective skin barrier; severe burns lead to decrease in neutrophil function
Hospitalization - at risk for nocosomial infections
A 12 year old child is severely burned in a house fire. He was hospitalized for over a month with 3rd degree burns on his leg. About a week after admission, he developed an infection of the burned areas. Blue-green pus was associated with the infection.
Which organisms are the most common causes of burn infections?
Pseudomonas aeruginosa (wet areas)
Staphylococcus aureus (skin)
Staphylococcus epidermidis (skin)
Streptococcus pyogenes (skin, mucous membranes)
Candida (skin, mucous membranes)
Aspergillus (soil, dark & damp areas - spores)
*burn infections often polymicrobial*
Pseudomonas on nutrient agar
Aspergillus
Name the following microbes isolated from the 12 y/o burn patient’s blood and/or exudate.
- Gram (+) cocci, catalase (+), coagulase (-)
- Gram (+) cocci, catalase (+), coagulase (+)
- Gram (-) rod, greenish colored colonies on nutrient agar
- fungus in below image
- Staph epidermidis
- Staph aureus
- Pseudomonas
- Aspergillus
Of the 4 microbes isolated from the 12 y/o burn patient’s wounds, what was isolated from his burn? What was isolated from his blood?
Burn - Pseudomonas, Staph epidermidis
Blood - Pseudomonas, Staph aureus, Aspergillus
How did the 12 y/o burn patient become infected?
Skin colonization - Staph
Hospital environment - Pseudomonas, Aspergillus
Describe the pathogenesis of burn wound infections.
Bacteria that colonize skin are first to invade wound (within days). Pseudomonal & fungal infections occur ~1 week after hospitalization. Important virulence factors include resistance to phagocytosis & enzymes that facilitate invasion.
Describe the epidemiology of Pseudomonas.
Ubiquitous
Resistant to some common disinfectants
Antibiotic resistance is common
Causes infections in CF, catheterized, burn, and intubated patients
What are common locations for Pseudomonas infections?
Skin & musculocutaneous tissues
Respiratory tract
CNS
Localized
Blood (bacteremia)
Heart (endocarditis)
Urinary tract (UTI)
Ecthyma gangrenosum - consequence of Pseudomonas septisemia; hemorrhagic necrosis of the skin
How would you treat your 12 y/o burn patient who is positive for Staph epidermidis, Staph aureus, and Aspergillus?
MRSA - Vancomycin, Linezolid, Streptogramin
MSSA - Vafcillin/Oxacillin/Dicloxacillin, 1st/2nd gen. cephalosporin, Clindamycin
Pseudomonas - Extend spectrum penicillin + beta-lactamase inhibitor, carbapemen, Monobactam, fluoroquinolones, Ceftazidime, Cefepime, aminoglycosides
Aspergillus - Voriconazole, Caspfungin
So…Vancomycin + Amp B until data comes back
A newborn baby had a fever and appeared septic. Blood cultures grew a gram-positive coccobacillus that was weakly beta-hemolytic, was motile and grew at 4C. A diagnosis of Listeria monocytogenes was made, and the infection was transmitted from the mother prior to birth.
Why is an infant considered immune compromised?
Decreased: production of neutrophils, killing by phagocytes, complement levels, NK cell activity, in vitro lymphocyte proliferation, cytokine production by lymphocytes, CTL responses, expression of CD40L, production of Ig (especially IgG & IgA).
A newborn baby had a fever and appeared septic. Blood cultures grew a gram-positive coccobacillus that was weakly beta-hemolytic, was motile and grew at 4C. A diagnosis of Listeria monocytogenes was made, and the infection was transmitted from the mother prior to birth.
How did the infant become infected?
Fetal infection can occur from:
transplacental transmission
ascending infection through ruptured amniotic membranes
during birth through an infected birth canal
A newborn baby had a fever and appeared septic. Blood cultures grew a gram-positive coccobacillus that was weakly beta-hemolytic, was motile and grew at 4C. A diagnosis of Listeria monocytogenes was made, and the infection was transmitted from the mother prior to birth.
What were the symptoms, if any, in the mother?
Nausea, vomiting, diarrhea, fever, malaise, back pain, and headache
Many pregnant women can carry Listeria asymptomatically in their GI tract or vagina
Maternal infection with Listeria can affect pregnancy by causing chorioamnionitis, premature labor, spontaneous abortion, or stillbirth
A newborn baby had a fever and appeared septic. Blood cultures grew a gram-positive coccobacillus that was weakly beta-hemolytic, was motile and grew at 4C. A diagnosis of Listeria monocytogenes was made, and the infection was transmitted from the mother prior to birth.
Where is the organism found in nature - how did the mother become infected?
Widely distributed in nature - intestinal tracts of many mammals; most commonly associated with ingestion of prepared meat, dairy products, unwashed raw vegetables, and seafood. Soft cheeses and unpasteurized milk have bee nthe most frequently incriminated dairy products.
A newborn baby had a fever and appeared septic. Blood cultures grew a gram-positive coccobacillus that was weakly beta-hemolytic, was motile and grew at 4C. A diagnosis of Listeria monocytogenes was made, and the infection was transmitted from the mother prior to birth.
How would you treat the baby?
Ampicillin + Gentamicin
A 42 year old woman is hospitalized with pneumonia. Her history is significant for long term corticosteriod use for severe asthma. A sputum gram stain revealed gram-positive bacilli, coccobacillary cells and branching filaments. A modified acid-fast stain showed the organism to be partially acid-fast. The organism was identified as Nocardia sp.
What made this patient susceptible to this infection?
Corticosteroids - long-term use
A 42 year old woman is hospitalized with pneumonia. Her history is significant for long term corticosteriod use for severe asthma. A sputum gram stain revealed gram-positive bacilli, coccobacillary cells and branching filaments. A modified acid-fast stain showed the organism to be partially acid-fast. The organism was identified as Nocardia sp.
What is the source of the bacteria?
Ubiquitous in soil and water
A 42 year old woman is hospitalized with pneumonia. Her history is significant for long term corticosteriod use for severe asthma. A sputum gram stain revealed gram-positive bacilli, coccobacillary cells and branching filaments. A modified acid-fast stain showed the organism to be partially acid-fast. The organism was identified as Nocardia sp.
What are the unusual features of this bacteria?
Cell walls contain mycolic acid, thus pick up acid fast stain
A 42 year old woman is hospitalized with pneumonia. Her history is significant for long term corticosteriod use for severe asthma. A sputum gram stain revealed gram-positive bacilli, coccobacillary cells and branching filaments. A modified acid-fast stain showed the organism to be partially acid-fast. The organism was identified as Nocardia sp.
How should she be treated?
TMP/SMX is drug of choice; other antibiotic combinations can be used
Nocardia
A 42 year old woman is hospitalized with pneumonia. Her history is significant for long term corticosteriod use for severe asthma. A sputum gram stain revealed gram-positive bacilli, coccobacillary cells and branching filaments. A modified acid-fast stain showed the organism to be partially acid-fast. The organism was identified as Nocardia sp.
If patient has pulmonary nocardosis, what symptoms would you expect to find?
Lobar pneumonia with abscess formation
May mimic TB clinically - fever, weight loss, chest pain
Infection can spread from lung to other sites via blood
A 23 year old AIDS patient had fever, night sweats, fatigue and diarrhea for the past 3 months. Over that time, she has lost 22 pounds and is short of breath. Her CD4 count has been below 50/cmm for the past 6 months and her viral load is 55,000/cmm. Routine blood cultures were negative after 48 hours; however, growth was seen after 10 days. DNA probes identified the organism as belonging to the Mycobacterium avium complex.
What are the diagnostic features of this organism?
Group of related organisms - MAC
Bacilli-weakly gram (+), strongly acid fast
MAC infection in aids patient - disseminated acid fast rods in tissue
A 23 year old AIDS patient had fever, night sweats, fatigue and diarrhea for the past 3 months. Over that time, she has lost 22 pounds and is short of breath. Her CD4 count has been below 50/cmm for the past 6 months and her viral load is 55,000/cmm. Routine blood cultures were negative after 48 hours; however, growth was seen after 10 days. DNA probes identified the organism as belonging to the Mycobacterium avium complex.
What are the sources of this organism?
Infect many bird & mammal species
Ubiquitous - in water & soil
Infection thought to occur by ingestion or inhalation
Describe the pathogenesis of disseminated MAC infection.
Enters immunocompromised person via ingestion/inhalation - infects resting macrophages of mucosal epithelium - carries organism throughout body (lymphatic sites) - replicates to very high numbers within macrophages within various tissues - infected macrophages secrete cytokines - cytokine storm
A 23 year old AIDS patient had fever, night sweats, fatigue and diarrhea for the past 3 months. Over that time, she has lost 22 pounds and is short of breath. Her CD4 count has been below 50/cmm for the past 6 months and her viral load is 55,000/cmm. Routine blood cultures were negative after 48 hours; however, growth was seen after 10 days. DNA probes identified the organism as belonging to the Mycobacterium avium complex.
What diseases does it cause in immune-competent individuals?
Pulmonary disease in persons with underlying lung conditions, smokers
A 23 year old AIDS patient had fever, night sweats, fatigue and diarrhea for the past 3 months. Over that time, she has lost 22 pounds and is short of breath. Her CD4 count has been below 50/cmm for the past 6 months and her viral load is 55,000/cmm. Routine blood cultures were negative after 48 hours; however, growth was seen after 10 days. DNA probes identified the organism as belonging to the Mycobacterium avium complex.
How is it treated?
In AIDS patients: Clarithromycin/Azithromycin + Ethambutol
A 23 year old AIDS patient had fever, night sweats, fatigue and diarrhea for the past 3 months. Over that time, she has lost 22 pounds and is short of breath. Her CD4 count has been below 50/cmm for the past 6 months and her viral load is 55,000/cmm. Routine blood cultures were negative after 48 hours; however, growth was seen after 10 days. DNA probes identified the organism as belonging to the Mycobacterium avium complex.
Could the infection have been prevented in this patient?
AIDS: yes - prophylaxis with Clarithromycin or Azithromycin when CD4 count falls < 50/cmm
Yeast on India ink stain
Musculocutaneous ulcers in the mouth; skin lesion due to Histoplasma
A bronchoalveolar levage specimen stained with methenamine silver revealed trophozoites and cysts.
Pneumocystis jiroveci
