Peritonitis: finding success by evaluating the failures

In the past 15 years peritonitis rates in patients on peritoneal dialysis (PO) have declined significantly, frorn > 1.6 episodes/patient year in the early 1980s to ~ 0.35 episodes/patient year according to recent reports (1, 2). This change may reflect changes in dialysis techniques as well as technical advances in connectology and PO systems that have evolved with increasing experience (1, 3). Nevertheless, peritonitis continues to be the leading complication experienced by patients maintained by PO (4, 5). It remains one of the primary reasons for technique failure, accounting for 27-55% of patients discontinuing peritoneal dialysis (4-6). Most infections are due to gram positive pathogens, predominantly S. epidermidis, suggesting "touch" contamination, perhaps from poor technique (7). This may be an oversimplification, but is how most nephrologists approach the problem and evaluate new products for improving peritonitis rates. To improve the technical success of PO, nephrologists have sought to identify risk factors for peritonitis, thus providing an opportunity for intervention. Recent reports (3, 6, 8) have identified several demographic, psychosocial, and technical features that influence the potential for peritonitis. These include race, level of education, living arrangements, and the PO system used. Racial differences in peritonitis rates have long been recognized (3, 4, 6, 8). The national CAPO registry found that black patients had a significantly higher risk of failing PO than whites, this being associated with higher peritonitis rates (4). The relative risk of peritonitis in black patients is 2': 1.6 times that of whites, independent of other demographic features (3, 6, 8). When rates of infection are broken down by organism, peritonitis rates for S. epidermidis are essentially twice as high in black patients as in whites (9, 10). The reason for this difference is unclear. Several factors, immunologic or psychosocial, may playa role and warrant further study (4, 6). The impact of psychosocial forces on peritonitis rates and the overall success of peritoneal dialysis is of great interest, but because of its complexity is difficult to study. One may be left with evaluating these forces indirectly by looking at social markers of "achievement" (implying better compliance) such as education, employment, income, living arrangements, social behaviour, and habits. Studies evaluating these features are limited in number and in the comprehensiveness with which these features are assessed, and are not always in agreement. A recent multivariate analysis of over 1500 patients assessed the impact socioeconomic factors including years of education, student status, housing ownership, living arrangements, employment status, and substance abuse, on the risk of peritonitis (8). It found that home ownership, student status, and substance abuse were factors that independently effected peritonitis rates. Patients who were home owners had a 20% lower risk (relative risk of 0.8) of peritonitis compared to those who rented. Substance abuse and student status were associated with an increased relative risk of peritonitis of 1.9 and 2.4 respectively. In other studies, the level of education attained was shown to have a negative correlation with peritonitis rates, lesser educated patients having higher peritonitis rates and poorer technique survival (5, 6). The assumption is that the increased risk for peritonitis in these patients is a result of a greater likelihood for mishap or non-compliance with technique, leading to increased infections with pathogens associated with touch contamination. In fact, the S. epidermidis peritonitis rates are over 50% higher for patients with ~ 8 years of education as compared to that for patients with 2': 13 years (9). By recognizing high risk patients, the nephrologist has the opportunity to make adjustements in training techniques and intensity of followup to assure an optimal understanding of and compliance with PO methods. The greatest impact on peritonitis rates, however, has been from advances in PO systems and connectology. These have semplified the procedure, and lowered S. epidermidis peritonitis rates (1). Disconnect systems using "Y" tubing decrease the potential for infection from touch contamination by allowing a "flush before fill" of the system, and have been given credit for much of the improvement in peritonitis rates (7). Peritonitis rates reported for patients on V-disconnect systems are 50% of those for standard spike systems (0.56 vs 1.2 episodes/pt yr) and are due predominantly to a reduction in S. epidermidis peritonitis (9, 11, 12). With the recent introduction of twinbag systems, the increased ease of performing exchanges, along with fewer connections, has resulted in peritonitis rates as low as 0.26 episodes/pt yr (2, 13). Automated peritoneal dialysis (APO) systems have further increased the probability of remaining peritonitis free (6, 14). Infection rates for virtually every microorganism (predominantly S. epidermidis infections) are signifi-