Total Number of Cases that do not Result in Death
We obtained the number of cases per year from the literature on HABP/VABP. HABP is not a reportable illness, and diagnosis may be complicated due to overlap with other respiratory tract infections, especially for mechanically ventilated patients; therefore, determining incidence for HABP and VABP is difficult (American Thoracic Society; Infectious Diseases Society of America, 2005). However, many sources cite available data suggesting that these infections occur at a rate of 5 to 10 cases per 1,000 hospital admissions (American Thoracic Society; Infectious Diseases Society of America, 2005; McEachern & Campbell, 1998), or roughly 300,000 cases per year, as McEachern & Campbell (1998) report. To get a more up-to-date estimate, we applied this rate to the 36.1 million inpatient discharges in 2009 (from the National Hospital Discharge Survey), which yields a range of 180,500 to 361,000 HABP/VABP cases per year, with the midpoint of the range equal to 270,750.
According to a 2007 public health report (the same one used to estimate the number of hospital-acquired CUTI cases), there were 250,205 cases of healthcare-associated pneumonia in 2002 (Klevens, et al., 2007), which is equivalent to a rate of 87.0 per 100,000 population. Applied to the 2011 U.S. population, this rate results in an estimated 272,598 cases for the year 2011. Though the 2007 report is not specific with regard to the types of infections that are included, the estimate of 272,598 cases per year is very close to the midpoint of the range calculated above (270,750). It is also similar to the 300,000 figure reported by McEachern & Campbell (1998). Therefore, we determined that 272,598 was a reasonable point estimate of HABP/VABP cases in 2011. Subtracting the total number of deaths (81,779) from this estimate (see Section 220.127.116.11), results in 190,818 surviving HABP/VABP hospital patients.
QALYs Lost per Case
From the Tufts database, we found a QALY weight of 0.83 for VABP (Shorr, Susla, & Kollef, 2004), which we then adjusted by period of illness.
As HABP/VABP occur, by definition, in patients who are already hospitalized for other conditions, it is necessary to determine the length of time by which the episode of HABP or VABP extends the patient’s stay (as opposed to the entire length of stay due to all conditions from which the patient suffers). According to the literature, HABP/VABP lengthens the period of hospitalization by 7 to 10 days (McEachern & Campbell, 1998; Sampathkumar, 2009), so we use the midpoint of this range for the purposes of our calculations (8.5 days). Though there may be some outpatient recovery time following hospitalization for patients who have suffered from HABP/VABP, that information is not readily accessible in the literature, perhaps because it is so difficult to distinguish between recovery time for HABP/VABP and recovery time for the patient’s underlying illness(es). Therefore, we do not include any outpatient recovery time in our estimates. Using 8.5 days as the illness period, we calculated lost QALYs as:
Total QALYs Lost due to Morbidity
Given that lost QALYs per HABP/VABP case is 0.00396 and the total number of HABP/VABP cases that do not result in death in the US is around 191,000, we computed the total annual QALYs lost due to HABP/VABP morbidity to be 756 in the US.
To calculate VSLY-based illness costs (for patients who do not die), we first selected an appropriate VSLY based on average patient age, as we do not have a breakdown of incidence by age group from the literature or other sources (as discussed above). The VSLY for people aged 55 to 62 is $290,150, which is then multiplied by the average lost QALYs per patient (0.00396) to arrive at $1,149 per patient. The total morbidity cost due to HABP/VABP was then computed at $219.2 million (= $1,149 × 190,818) per annum.