Volume 11, Number 06

PITFALLS IN URINARY MICROBIOLOGY On occasion bacteriuria may respond to an empirically chosen antibacterial agent yet the sensitivity report from the laboratory indicates that the organism is resistant to the agent. This anomaly is the result of tubular concentration of the antibacterial to levels often 50 to 100 times that expected and tested as serum concentration. If the drug works, continue to use it, but remember that it will not be effective if the infection has ascended to the kidney or is otherwise systemic. A second problem is the urinalysis which shows significant numbers of bacteria and/or leucocytes or leucocyte esterase in the symptomatic (usually female) patient in whom the culture is negative. Three possible explanations are: The patient has taken an antibacterial (even a single dose). The urinalysis findings and symptoms are caused by a vaginitis. The bacteriuria is of a degree less than the established lower limit for which the laboratory normally tests. The solution to the first two problems is obvious. That to the third is to request that the laboratory report low level bacteriuria on that particular patient.

WHOOPING COUGH The incidence of Pertussis has doubled for the second year in a row. Both Pertussis and the commonly present Mycoplasma pneumoniae tend to produce dry, spasmodic coughing to the point of near vomiting. This must be elicited in the clinical history. The defective laboratory test is a complicated cultural technique. It is more practical for most physicians and patients to treat presumptively with Erythromycin or a tetracycline (the latter in adults only) and to test the patient serologically for both species at least a week after the onset of the illness.

STOOL PARASITOLOGY How many specimens to order? Parasitology is a test frequently forgotten in the evaluation of bowel dysfunction. One need not have travelled to exotic countries to be infected. At least 95% of the world's bowel problems are infectious. It makes sense to look for infectious agents including parasites before proceeding to more costly or invasive procedures. In low grade infections or carrier states, the passage of cysts and ova may be scanty or intermittent. It is for this reason that the usual format for testing is to take a sample from each of three different bowel movements (they need not be from consecutive bowel movements). Three samples are considered optimal, since a single specimen has about a 60-70% potential to yield parasites. Thus, three specimens will yield a 93-97% probability of recovery. The stool should be collected by defecating directly into a large, clean wide-mouthed container (such as a clean plastic margarine tub or cottage cheese container). Specimens must not be taken from the toilet bowl. From this stool, a pea-sized specimen should be taken and placed into the specimen bottle containing the SAF fixative (provided by the lab). If the stool is watery, the amount put into the fixative should be equivalent to about a teaspoon. In both cases, the specimen bottle should be capped tightly and gently shaken to suspend the fecal material. After this is done, the specimen may be kept at room temperature. It is important to stress that the three specimens must be obtained from three separate and distinct bowel movements. The specimens can be held until all three are collected and then brought to the lab or doctor's office. On the other hand, if one is dealing with a severe diarrhea, a single specimen will often suffice and should be brought in immediately to avoid delay in therapy. It is appropriate to test: Asymptomatic travellers about 6 weeks after their return (to allow for incubation periods). Symptomatic travellers (including rural North America) to be done immediately. Food handlers. Family contacts of parasitized individuals. Nursery school attendees, and Any individual with persisting bowel dysfunction.

HEMATURIA INVESTIGATION Hematuria is considered to be present when there are 5 or more red blood cells per high power field in a centrifuged urine sample. Test reagent strips detect both hemoglobin and myoglobin. The test is positive down to 0.05 to 0.30mg hemoglobin/dl. The latter level is equivalent to 10 lysed red cells/ml. Test strips will not detect intact red cells, however lysis of red cells begins occurring soon after they enter the urine. The clinical investigation of hematuria can be considered to fall into 3 categories because the approach differs with each. These categories are: Adult Child Traumatic Below is a simple plan for the investigation of the first of these three.

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