EXERCISE 1 - Duke University
Microbiology Infectious Disease Case Studies
Pathology Small Group
2012
Compiled by the Faculty
Department of Molecular Genetics and Microbiology
Modified by the Faculty
Department of Pathology and Laboratory Medicine
Duke University Medical Center
Durham, North Carolina
MENINGITIS
CASE HISTORY: An 18-year old college freshman presents to student health with a fever, malaise, a purpuric, non-blanching rash and nuchal rigidity. A lumbar tap was performed with the following results: cell count was 300, 100% PMN; glucose 10mg/dl; protein 100 mg/dl; and Gram stain revealed numerous PMN’s with intracellular gram-negative diplococci.
1. What is the most likely organism in this case?
2. What type of medium would be required to isolate this organism?
CASE HISTORY: A 13 month-old child was running a temperature at home when he suddenly had a grand mal seizure with shaking of arms and legs. The mother called 911 and the EMT's found the child limp, unresponsive. In the emergency room he had a second seizure. He was lethargic, neck was supple, temperature was 39.5(C (103.1(F). Blood cultures and lumbar tap were performed. CSF findings were as follows: cell count was 4000, 95% PMN's; glucose 20 mg/dl; protein 125 mg/dl; Gram stain revealed numerous PMN’s and occasional coccobacillary Gram-negative rods. Social history revealed that the family had immigrated from another country two months prior.
1. What is the most likely organism in this case?
2. What is the significance of the social history to the organism that was isolated?
CASE HISTORY: The patient was a 34-year old HIV-positive male with a CD4 count of 80/(L. The patient had a 1-week history of progressively worsening headache, photophobia, lethargy, and fevers to 38.5°C. On the morning of his admission, he became confused, disoriented, and ataxic, having fallen three times. On physical examination, he was lethargic and could only answer a few questions before falling asleep. His vital signs were all within normal limits. Chest examination and radiograph were normal. He had a head CT scan, which was also normal. Because of his decline in mental status and history of headache and photophobia, a lumbar puncture was done. It showed 32 WBC/(L with 89% lymphocytes and 6% monocytes, a glucose level of 22 mg/dl, and protein of 89 mg/dl. Gram stain of his CSF revealed spherical yeasts. Serum and CSF tests for the presence of a specific antigen were positive. The organism was recovered from cultures of his CSF and blood.
1. What is the organism most likely to be causing his illness?
2. Are his CSF cell count and chemistries consistent with infection with this organism?
3. What other organisms are frequently seen causing CNS infections in this patient population?
4. What is the specific antigen that was found in his serum and CSF?
5. In which clinical situations can this antigen test be used to help manage patients.
6. What other organism will give a positive reaction in this test?
7. How did this patient become infected?
8. How should this patient be managed to prevent relapses with this organism in the future?
DISCUSSION
Infections of the central nervous system constitute the real emergency situation in clinical microbiology. Patients can die in a matter of hours of presenting to the emergency room. The only cost effective, truly rapid, microbiological test that can effect treatment is the Gram stain. In both cases presented here the Gram stain was positive for bacteria. In one study from Bowman Gray School of Medicine, the Gram stain was positive in 80 to 100% of the cases of N. meningitidis, S. pneumoniae and H. influenzae, but only positive 25% of the time for group B streptococcal and other bacterial meningitides.
Other surrogate markers of infection are the concentration of protein, glucose, and the type and number of cells in the CSF.
ENDOCARDITIS AND IATROGENIC INFECTIONS
CASE HISTORY: The patient is a 45-year old man who had his mitral valve replaced with a Starr-Edwards valve one month ago. He presents with a temperature of 38.6(C (101.5(F), splinter hemorrhages in his nails, and a new heart murmur. Trans-thoracic echocardiogram revealed 2 cm vegetation on the valve. A total of 3 blood cultures were taken over a two hour period of time and sent to the laboratory. After 10 hours the laboratory notified the physician that 2 out of 3 of the blood cultures grew Gram-positive cocci in clusters.
1. What is the most likely organism in this case?
2. What are the pre-disposing factors which led to the patient becoming infected?
3. What is the most likely source of the organism?
3. Was the correct or incorrect number of blood cultures drawn on this patient?
4. Why did the clinician collect the cultures over a two hour time period?
CASE HISTORY: The patient was a 25 year-old international graduate student. The patient presents with a temperature of 38(C (100.4(F), malaise, and generalized weakness. Significant laboratory findings include a white count of 16,700 with 85% PMN's and negative Monospot test. Physical exam revealed a well-nourished young male in moderate distress. Lungs were clear and there were normal bowel sounds. A grade II/VI grade systolic murmur was heard over the left sternal border and an echocardiogram revealed a 1 cm vegetation on the aortic valve. Past medical history was significant for a history of rheumatic fever and extensive dental work 2 months prior to presentation. Three blood cultures were drawn and sent to the laboratory. The patient was admitted and begun on what was later determined to be the appropriate antibiotic. After 24 hours all three cultures were positive for a Gram-positive coccus in chains.
1. What is the most likely organism in this case?
2. What are the pre-disposing factors which led to the patient becoming infected?
3. What is the most likely source of the organism?
4. What was the appropriate antibiotic that was used on this patient?
CASE HISTORY: This 67-year old woman was admitted with a recurrence of her poorly differentiated squamous cell carcinoma of the cervix. She underwent extensive gynecologic surgery and was maintained postoperatively on broad-spectrum intravenous antibiotics. The patient had a central venous catheter placed on the day of the surgery. Beginning 3 days postoperatively, the patient had temperatures of 38.0°C to 38.5°C, which persisted without a clear source. On day 8 postoperatively, she had a temperature of 39.2°C. Cultures of blood and of the tip of the central line grew a yeast that was ovoid and reproduced by budding. The organism was recovered on sheep blood agar medium.
1. What is the differential diagnosis of this patient’s infecting organism?
2. The organism was subsequently shown to form germ tubes. What is the organism?
3. Is this organism part of the normal flora in humans?
4. What factors in the patient’s history predisposed her to infection with this organism?
5. What was the likely source of the organism causing this infection?
DISCUSSION
Bacteremia occurs during the course of many diseases such as pneumonia, urinary tract and wound infections, meningitis and even some diarrheal diseases. At times, as in the two cases in this exercise, the vascular system is the primary site of the infection.
The vascular system usually does not serve as the primary site of infection unless there is some underlying condition. In case one, the patient had surgery with a foreign body replacing the native valve. Foreign bodies and manipulation predispose one to infections of the vascular system. In this case, this infection was acquired during surgery and the organism, coagulase negative Staphylococcus, is a major cause of surgical infections when a foreign body is present. In the second case, the damage to the vascular system was due to rheumatic fever which damages the lining of the heart and heart valves leaving them prone to deposition of fibrin. When organisms gain access to the blood stream, as in a dental procedure, they deposit
on the fibrin and develop into the vegetation which consists of layers of organism and fibrin. The viridans streptococci isolated in the second case are the most common cause of bacterial endocarditis involving native valves.
In both cases the organisms live in the vegetation and are shed intermittently into the blood stream. At times pieces of the vegetation break off and are trapped in capillaries throughout the body. These can lead to infections in other organs, such as the brain, where they may form abscesses. Blockage of the capillaries also causes leakage and splinter hemorrhages. These can occur anywhere in the body but are most easily observed in the nails and conjunctiva.
Regardless of the source of the organisms in the blood, they are often present in low numbers and the presence is not constant over time. The average adult who is bacteremic has only 1 to 10 organisms/1 ml of blood. This requires that one obtains a large volume of blood, usually 10 to 20 ml, and collects at least two to three cultures to diagnose more than 95% of patients with bacteremia. A single blood culture only detects about 85 to 90% of bacteremic patients. Since the number of organisms in the blood is usually low, the entire volume of blood is cultured in a broth medium. A set of blood cultures may consist of two aerobic media or one aerobic and one anaerobic medium with 5 to 10 ml added to each bottle of medium. (The volume may vary with the system being used in the laboratory.) Taking of more than one set of blood cultures over time also aids in determining the significance of an isolate. Coagulase negative staphylococci are present on skin and single isolates frequently indicate a “contaminated” blood culture; whereas, multiple isolates over time probably indicate that the isolation of coagulase negative staphylococci is significant. In case one, the multiple isolates over time, coupled with a clinical history consistent with endocarditis, make it easy to determine the significance of the coagulase negative Staphylococcus.
When the blood culture bottles reach the laboratory they are usually incubated in instruments that monitor bacterial growth by measuring the CO2 produced or the changes in atmospheric pressure in the bottles. These instruments generally measure the changes every 6 to 12 minutes and are termed continuous monitoring instruments. These instruments can detect positive bloods in an average of 18 hours compared to the 42 hours needed for detection by manual methods or older instrumentation. In some studies, positive bottles were detected in as little as 4 to 6 hours with continuous monitoring instruments.
When a significant change is detected in the bottle, the instrument signals it as the positive. The technologist removes the bottle, performs a Gram stain and notifies the clinician of the results. The bottle is also subcultured to agar plates to isolate the organism for identification and susceptibility testing. Most laboratories incubate bottles for 5 days before signing them out as negative.
URINARY TRACT INFECTIONS
CASE HISTORY: A 25-year-old woman presents with left flank pain, frequency and burning on urination. Urinalysis reveals 2+ white blood cells, a positive nitrite test and 2+ bacteria. No casts were seen. A urine culture was submitted.
1. What is the likely organism in this case?
2. What does the colony count of the organism in the urine specimen indicate?
3. What do the urinalysis findings indicate?
4. Young women have more urinary tract infections than young men. Why?
5. What Gram-negative rods are lactose fermenters?
6. Which are the most common causes of UTI?
CASE HISTORY: 75-year-old male nursing home patient had been complaining of urine retention and the feeling of being unable to completely empty his bladder. The patient also complained of feeling flushed and was agitated. His temperature was 39(C. Physical exam revealed an enlarged prostate.
1. What is the likely organism in this case?
2. What would the laboratory report say about the colony count of the organism in the urine specimen?
3. As men age, the frequency of UTI's increase to that of women. Why?
4. If the organism is characterized as a Gram-positive coccus, growing in short chains, and catalase negative, what is the most likely organism?
5. What therapeutic/resistance problems may be relevant in this case?
DISCUSSION
The urinary tract infection (UTI) is one of the most common bacterial diseases. Patients of both sexes and all age groups are affected. Proper management of these infections requires an understanding of the number and kinds of bacteria involved.
Most UTI’s result from ascending infection by organisms introduced through the urethra, and less commonly via the hematogenous route. In hospitals, urinary tract infections are the most common form of nosocomial infection. Acute infections are more common in females than in males because of the shorter urethra and greater likelihood of its contamination. A bacterial count of 100,000 or more organisms per ml of urine from patients who are asymptomatic for urinary tract infection is considered to be a significant bacteriuria and suggestive of infection. This is because urine is an excellent culture medium for most organisms that infect the urinary tract, and because growth occurs in vivo in the urine itself, resulting in high bacterial counts in established infections. In contrast, contamination from the external genitalia, in the absence of infection, usually contributes less than 1,000 organisms per ml in properly collected and transported specimens.
UTI’s may vary in severity from an unsuspected infection to severe systemic diseases involving microbial invasion of any of the tissues of the urinary tract. Infection may involve a single site, such as the urethra (urethritis), prostate (prostatitis), bladder (cystitis), or kidney (pyelonephritis), or more than one site, as frequently occurs.
The most common sites of UTI in women are the urethra and urinary bladder, but infection from these sites may spread to the kidneys. Enterobacteriaceae are responsible for nearly all nongonococcal urethrocystitis, with Escherichia coli accounting for about 90% of these cases. Other organisms associated with urinary tract infections in the female include Klebsiella, Enterobacter, Proteus, Pseudomonas, group B Streptococcus, Enterococcus, Staphylococcus aureus, and Candida.
In the male, chronic bacterial prostatitis is a common disease, difficult to cure, and is often responsible for relapsing urinary tract infections. It is usually caused by Gram-negative bacilli. E. coli is responsible for 80% of the cases, the remainder being caused by Klebsiella, Proteus, Pseudomonas, or Enterobacter.
Pyelonephritis is an inflammatory process involving both the pelvis and parenchyma of the kidney, which may become chronic and lead to extensive renal destruction. The clinical diagnosis of pyelonephritis is frequently overlooked because of the absence of symptoms. There is often a correlation between a bacteremia and an unsuspected pyelonephritis. An indwelling catheter often leads to the development of a bacteremia, frequently accompanied by a Gram-negative rod septicemia. The demonstration of bacteria by culture is the only reliable means of making a definitive diagnosis. In acute pyelonephritis, E. coli is the etiologic agent in up to 90% of the patients. The remaining cases are caused by Klebsiella, Enterobacter, Proteus, and enterococci.
Specimen Collection. Care in collection, storage, and transport of urine specimens for bacteriologic examination is of utmost importance. Contaminating bacteria from the perineum can multiply in specimens standing at room temperature and invalidate the results. Urine specimens may be collected by the: (1) clean-voided mid-stream technique, (2) catheterization, and occasionally (3) suprapubic aspiration. The clean-voided specimen is recommended wherever possible because it eliminates the risk of infection.
Bacteriologic Examination. The basic procedure consists of two parts: (1) estimation of the total number of microorganisms per ml of urine, and (2) isolation, identification and antimicrobial susceptibility testing (where indicated) of the predominant microorganisms.
PULMONARY INFECTIONS
CASE HISTORY: A 42-year-old North Carolina man was in good health until 2 months prior to admission, when he developed a low-grade fever, myalgias, and a nonproductive cough. He was given oral erythromycin by his local physician. After 2 weeks of therapy, his condition had not improved. A chest radiograph revealed “right middle lobe air space disease,” and therapy with oral ampicillin was initiated. Over the next month, his condition worsened. He noted daily fevers, chills, night sweats, and weight loss of several pounds. One month prior to admission, a chest radiograph showed consolidation of the right middle lobe. A PPD skin test was negative with positive controls, and an oral antibacterial antibiotic was prescribed. The patient’s symptoms continued, and he was admitted to the hospital. The patient had an unremarkable travel history and no animal exposure, was a non-smoker, and had no HIV risk factors. He worked for the power company cutting tree limbs and trees. On physical examination he was febrile to 38.3°C. The skin examination was notable for a tender, raised, erythematous papule (1 sq. cm.) on the bridge of the nose. A chest radiography and subsequent computed tomogram (CT) scan revealed a densely consolidated right middle lobe, a 3.5-cm subcarinal mass, and a small right hilar mass. Bronchoscopy was performed. KOH examination and acid-fast, modified acid-fast, and Gram stains were negative. Examination of the lesion using a silver stain demonstrated large, spherical budding yeasts with a broad base connecting the parent cell and the bud.
1. What is the differential diagnosis for this patient’s pulmonary disease?
2. Which organism is causing his illness?
3. What are its epidemiology and culture characteristics?
4. This patient’s lungs and skin were involved with this infection. Which other sites are commonly involved?
5. Was there any component of this patient’s history that might alert a physician to think of this organism?
6. Which organisms may be detected by a KOH examination?
7. Which organisms may be detected by an acid-fast stain?
CASE HISTORY: A 37 year old male, was admitted to Duke Hospital with an increased WBC and a peripheral smear consistent with acute leukemia. A bone marrow biopsy found 70-80% blast forms, diagnostic of acute myelomonocytic leukemia. The patient underwent induction chemotherapy, followed by a second bone marrow biopsy, which also revealed blast forms. After a second round of induction chemotherapy, he became profoundly neutropenic ( ................
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