Nitrites in the urine of people without any urinary symptoms

Recently I tested the urine of  a male patient who had fever for 4 days with no localising symptoms and signs. The urine showed a trace of protein, some leukocytes and red blood cells (less than 10 cells per high power field). The urine nitrite test was positive. I wondered if this patient really had urinary infection because, if not for the positive urinary nitrite, I might have considered the urine protein and cellular abnormalities as being the result of the fever and not the cause of the fever. This led me to read an article in the American Family Physician which gave me some information as to why the urinary nitrite test may be falsely positive. I have quoted the relevant extract below:

Nitrites normally are not found in urine but result when bacteria reduce urinary nitrates to nitrites. Many gram-negative and some gram-positive organisms are capable of this conversion, and a positive dipstick nitrite test indicates that these organisms are present in significant numbers (i.e., more than 10,000 per mL). This test is specific but not highly sensitive. Thus, a positive result is helpful, but a negative result does not rule out UTI.⁶ The nitrite dipstick reagent is sensitive to air exposure, so containers should be closed immediately after removing a strip. After one week of exposure, one third of strips give false-positive results, and after two weeks, three fourths give false-positive results.³⁶