Eventual symptoms were registered in the study protocol and a single voided specimen of urine was collected. A urine dipstick was analyzed and urine cultured from elderly individuals at nursing homes during a four-week period in the first months of 2003. The nursing homes were located in southwestern Sweden. The study was approved by the ethical committee of Gothenburg University. The data was collected along with another study evaluating dipstick urinalysis among elderly residents .
Individuals at the nursing homes, regardless of symptoms, were asked to participate. One single urine specimen was collected from each included, permanent elderly resident of 102 wards in 32 nursing homes. The following inclusion criteria were applied:
Permanent residence in nursing homes for elderly (regardless of gender).
No indwelling urinary catheter (as they always become bacteriuric).
Sufficiently continent to leave a voided urinary specimen (obtaining urinary specimens by catheterizing these individual would not be representative of clinical practice and furthermore unethical).
Present at the nursing home for elderly when the study took place.
No ongoing dialysis.
The following exclusion criterion was used:
For individuals with dementia the same inclusion/exclusion criteria were applied. However substantial incontinence among these individuals with dementia sometimes made it impossible to obtain a voided specimen of urine.
Statement of consent
Individuals were informed about the study verbally and in written text. Informed approval for participation in the study was collected from decision-capable individuals that chose to participate in the study.
A considerable number of the participants, however, consisted of individuals with varying degrees of dementia. If the individual had no possibility to comprehend the meaning of the study information and thereby had a reduced decision-capability, these individuals only participated as long as they did not oppose participation and under the condition that a relative/appointed representative did not oppose their participation after having taken part of the study information. Thus, in case of dementia, where the individual did not understand the provided information, a sample was taken only if permission was granted. This procedure was approved by the ethical committee, University of Gothenburg.
The attending nurse at the nursing home registered, in a study protocol, once for each individual according to carefully provided instructions, if any of the following symptoms had appeared or increased: restlessness, fatigue, confusion, aggressiveness or not being herself/himself, dysuria, urgency and fever. Depending on how long the symptoms had persisted or increased, they were divided into the following three groups: less than one week, more then one week but less than one month, more than one month but less than three months. A symptom was not registered if it had persisted unchanged longer than three months. The study protocol included whether the individual had ongoing or previous antibiotic treatment within the last month.
The personnel at the nursing home were instructed to collect voided urine specimens with as long a bladder incubation time as possible, preferably a mid-stream morning sample. Then, dipstick urinalysis was carried out at the nursing home. The attending nurses at the nursing home were carefully instructed to register presence or absence of symptoms in the study protocol before performing dipstick analysis and taking a urinary culture. Thus the evaluation of symptoms was not influenced by the results of the urine tests.
Immediately after the dipstick readings the urine samples were chilled before transport to the microbiological laboratory in Borås where urine specimens were cultured. The samples usually reached the laboratory within 24 hours.
Using sterile inoculating loops the microbiology laboratory fractionated 10 μl urine on the surfaces of two plates; a cystine-lactose-electrolyte deficient agar (CLED) and a Columbia blood agar base. Plates were incubated overnight (minimum 15 h) at 35-37°C. CLED plates were incubated in air and Columbia plates were incubated in 5% CO2. The latter was further incubated for 24 hours if no growth occured after the first incubation.
Growth of potentially pathogenic bacteria was usually considered positive if the number of colony-forming units per liter (CFU/mL) was ≥105. However, at signs of possible UTI such as positive nitrite dipstick, leukocyte esterase dipstick >1, fever, frequency, urgency or dysuria, the cut-off point was ≥103 for patients with growth of Escherichia coli and male patients with Klebsiella species and Enterococcus faecalis. For symptomatic women harboring the two latter species the cut-off level was ≥104.
Depending on how long symptoms had persisted, they were divided into the following three groups; less than one week, less than one month, and less than three months. To evaluate the statistical correlation between bacteriuria and presence of a symptom at group level logistic regressions were performed. The symptom was used as dependent variable and the outcome of the urinary culture, age and sex as independent variables. One regression was made for each symptom and duration. One regression was also made for each symptom merging time intervals to all occurring within three months.
To estimate clinical relevance of statistical correlations, the positive and negative etiological predictive value (EPV)  was calculated to evaluate the probability for a positive/negative culture to rule in or out that a symptom in a single individual is associated with a bacterial finding. These predictive values were considered clinically useful if their point estimate was ≥ 75% with a lower 95% confidence interval ≥ 50%.
Logistic regression is a more sensitive statistical method than EPV. It is common that regression shows statistical significance while positive EPV does not show that a positive test outcome is clinically relevant. The opposite can never occur. Negative EPV is less affected by asymptomatic carriers and will often be high in case of a negative test.
Epi Info version 3.3.2 (Windows version) (CDC, Atlanta, USA) was used for storing data and for logistic regression. EPV with confidence intervals was calculated using the EPV-Calculator version 1.12 .