Analytical Framework for Examining the Value of Antibacterial Products. 3.6.5.5 Cuti

04/15/2014

Total Number of Cases that do not Result in Death

Assessing the incidence of CUTI is difficult because urinary tract infection is not a reportable disease in the United States (Foxman, 2002).  Total number of cases per year was obtained from the literature on urinary tract infections.  We estimated cases of community-acquired CUTI separately from cases of hospital-acquired (nosocomial) UTI.

To arrive at a number of cases for community-acquired CUTI, we assumed that all inpatient hospitalizations where the primary diagnosis was urinary tract infection were cases of community-acquired CUTI.  Griebling and Freedmen (2007) analyzed the 2000 National Inpatient Sample and estimated a total of 403,814 inpatient hospital stays for men, women and children with UTI as the primary diagnosis in 2000.  They provide rates of inpatient stays by age and gender breakdowns.  For comparison, we replicated this analysis with the 2009 NIS using the list of ICD-9 codes for urinary tract infection provided by the authors.  For 2009, we estimated a total of 543,140 inpatient hospital stays for men, women and children with UTI as the primary diagnosis.  When divided by the 2009 U.S. population, this is equivalent to a rate of 17.7 per 10,000 population.  The National Hospital Discharge Survey (NHDS) (2009), available from the Centers for Disease Control and Prevention (CDC) website, arrives at a similar total of 575,000 discharges of patients treated for urinary tract infection in 2009, or a rate of 18.8 per 10,000 population.  For our calculations, we applied the 2000 rates of inpatient stays for men, women, and children to the U.S. population totals for those categories to arrive at a total an inpatient count of approximately 470,915 cases of community-acquired CUTI in 2011 (National Hospital Discharge Survey, 2009).

According to a 2007 public health report that uses data from the National Nosocomial Infections Surveillance (NNIS) system (conducted by the Centers for Disease Control and Prevention), supplemented by data from the National Hospital Discharge Survey and the American Hospital Association Survey, there were 561,667 cases of healthcare-associated urinary tract infection in 2002 (Klevens, et al., 2007), which is equivalent to a rate of 195.4 per 100,000 population.  Applied to the 2011 U.S. population, this rate results in an estimated 611,935 cases for the year 2011.

We subtracted the estimated deaths from the estimated total number of CUTI cases in 2011 to get surviving CUTI hospital patients (448,311 and 597,675 for community-acquired and hospital-acquired, respectively, for a total of 1,045,986 CUTI cases).

QALYs Lost per Case

From the Tufts database, we found a QALY weight of 0.73 as a mean utility weight for bladder infections (Gold, Franks, McCoy, & Fryback, 1998).  This value is relatively consistent with a 0.2894 disutility (0.7106 utility) for “chronic dysuria, vaginitis and other symptoms” from a different cost-utility analysis of UTIs in ambulatory women, which also lists a disutility of 0.3732 for pyelonephritis (Barry, Ebell, & Hickner, 1997).  As was done for other indications, we adjusted this weight by period of illness.

We calculated lost QALYs separately for community-acquired and hospital-acquired CUTI.  To calculate lost QALYs for community-acquired CUTIs, we used an average inpatient length of stay of 4 days.  This number represents a weighted average length of stay for adults 18 to 64 years of age, who represent the bulk of the working population.  Although there may be some outpatient recovery time following hospitalization for patients who have suffered complicated urinary tract infections, that information is not readily accessible in the literature, so outpatient recovery time is not included in these estimates.  Thus, the lost QALYs per patient for community-acquired CUTI were estimated as:

Formula 3.6.5.5-1

As nosocomial CUTIs occur, by definition, in patients who are already hospitalized for other conditions, it is necessary to differentiate the length of time by which the episode of hospital-acquired CUTI extends the patient’s stay from the entire length of stay due to all conditions from which the patient suffers.  According to the literature, nosocomial UTI lengthens the period of hospitalization by 1 to 4 days (Lai & Fontecchio, 2002), so we used the midpoint of that range (2.5 days) for the purposes of our calculations.  Again, although there may be some outpatient recovery time following hospitalization for patients who have suffered from nosocomial CUTI, that information is not readily accessible in the literature, perhaps because it is so difficult to distinguish between recovery time for CUTI and recovery time for the patient’s underlying illness(es).  Therefore, we do not include any outpatient recovery time in our estimates.  Using 2 days as the illness period, we calculated the lost QALYs per patient to be 0.00185 as:

Formula 3.6.5.5-2

Total QALYs Lost due to Morbidity

Given that lost QALYs per community-acquired CUTI case is 0.00296 and the total number of community-acquired CUTI cases that do not result in death in the US is around 448,000, we computed the total annual QALYs lost due to community-acquired CUTI morbidity to be 1,327 in the US. Similarly, the total annual QALYs lost due to hospital-acquired CUTI was computed as 1,106 (= 0.00185 × 597,675) per year. This yielded a total of 2,432 QALYs lost due to CUTI overall per annum.

Morbidity Cost

To calculate VSLY-based illness costs (for patients who do not die) we first calculated a weighted average WTP to avoid CUTI, which is equal to the VSLY weighted by CUTI incidence by age group in 2011.  To approximate the age distribution of CUTI incidence, we calculated the age distribution from 2000 HCUP data on inpatient stays with a primary diagnosis of UTI (U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, 2007).  The resulting weighted average VSLY is roughly $325,000 which is then multiplied by the average lost QALYs per patient (0.00296 and 0.00185 for community-acquired and hospital-acquired, respectively) to arrive at $961 per community-acquired CUTI patient and $601 per hospital-acquired CUTI patient, for a weighted average of $758 per patient for a CUTI case. The total morbidity cost due to CUTI was then computed at $792.9 million (= $758 × 1,045,986) per annum.

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