Factors Associated with Acute Kidney Infections in Healthy Women

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The summary below is from the full report titled "Risk Factors Associated with Acute Pyelonephritis in Healthy Women." It is in the 4 January 2005 issue of Annals of Internal Medicine (volume 142, pages 20-27). The authors are D. Scholes, T.M. Hooton, P.L. Roberts, K. Gupta, A.E. Stapleton, and W.E. Stamm.

What is the problem and what is known about it so far?

Women are particularly susceptible to urinary tract infections. Doctors usually designate infections of the urinary tract as those occurring in the kidney (pyelonephritis) or those occurring in the urinary bladder (cystitis). They know a great deal about factors that increase the risk for cystitis. Researchers have also studied hospitalized patients with pyelonephritis, but no studies have specifically evaluated risk factors for pyelonephritis in a population of otherwise healthy women living in the community (in which most cases of pyelonephritis occur).

Why did the researchers do this particular study?

To find out what factors were most likely to increase the risk for pyelonephritis in women.

Who was studied?

242 women between 18 and 49 years of age who belonged to a large health maintenance organization (HMO) in Washington state and who had received a diagnosis of pyelonephritis.

How was the study done?

The researchers compared women with pyelonephritis (case-patients) with 546 other women of similar age who belonged to the same HMO but who did not have pyelonephritis (controls). They interviewed each participant in the study (both case-patients and controls) by telephone and asked participants to respond to questions about their health and personal habits, including sexual behavior, contraceptive practices, history of urinary tract infections, and other medical conditions.

What did the researchers find?

Very few case-patients (18 of 242) were hospitalized for their pyelonephritis. Most women with pyelonephritis reported having had flank pain or fever in the 2 weeks before they received their diagnosis. Many women with pyelonephritis also reported symptoms suggestive of cystitis, such as a burning sensation on urination, increased frequency of urination, and urgency for urination. When compared with the control group, case-patients with pyelonephritis had a higher frequency of intercourse in the previous 30 days, were more likely to use a spermicide for contraception, and were also more likely to have had a new sex partner in the previous 12 months. In addition to sexual activity, they were more likely to report having had a urinary tract infection in the past 12 months and that their mother also had a history of urinary tract infections. Women with diabetes and women who reported that they leaked urine when they coughed or sneezed in the previous 30 days were also more likely to get pyelonephritis.

What were the limitations of the study?

Many of the findings depended on the participants' ability to remember and accurately report behavior and medical conditions over the previous year. In addition, information about urinary tract infections in the study participants' mothers was available only through the knowledge of their daughters.

What are the implications of the study?

Risk factors for pyelonephritis are the same as those for cystitis, a finding that supports the concept that these kidney infections usually result from bladder infections.