Total Number of Cases that do not Result in Death
We obtained the number of cases per year from the literature on acute otitis media. As ABOM is generally treated in the ambulatory care setting, we, like many other studies, considered it to be exclusively an outpatient disease and therefore used counts of outpatient visits to estimate the number of episodes per year (see, for example, Huang, et al., 2011). The primary sources used by many researchers to obtain information on acute otitis media visits are the National Ambulatory Medical Care Survey (NAMCS) and the National Hospital Ambulatory Medical Care Survey (NHAMCS), which are the only surveys of U.S. outpatient settings that collect drug prescribing information and allow for calculation of unbiased national estimates (Coco, Horst, & Gambler, 2009; Huang, et al., 2011).
To obtain an estimate of the number of cases per year, we used the information contained in Appendix A of the paper by Huang, et al. (2011) on healthcare utilization and the cost of pneumococcal disease. This study uses data from NAMCS/NHAMCS, to report by age group, the total number of outpatient visits for acute otitis media in which antibacterial drugs was prescribed. Based on information gathered from expert panels and other papers, Huang, et al. (2011) also include estimates of how often typical resolution of the disease occurs (as opposed to delayed resolution), the number of follow-up visits/visits per episode, and the frequency of over-diagnosis. Our first step in calculating the number of episodes per year was to determine the average number of outpatient visits per episode. To do this, we multiplied the probabilities associated with typical and delayed resolution by the number of visits associated with each possibility and arrived at approximately 1.2 visits per episode. Next, we adjusted the number of visits per year by subtracting the estimated proportion of visits that were over-diagnoses, and divided the resulting figures (broken down by age group) by the number of visits per episode, 1.2, to arrive at numbers of episodes per year by age group.
Across all age groups, we found there to be 12.6 million acute otitis media episodes for which antibacterial drugs were prescribed for the year 2004. Our finding is also consistent with the authors’ statements that there were 1.5 million cases of acute otitis media due to pneumococcus, and 12 percent of acute otitis media cases are due to pneumococcus (1.5 million/0.12 = 12.5 million total cases of acute otitis media). Using population estimates by age from the U.S. Census Bureau, we converted the total number of episodes by age group to rates and applied those rates to 2011 population figures to obtain a total number of cases for the year 2011, which we estimated to be 13.2 million. Since there are no deaths associated with ABOM (see discussion below), this is equivalent to the total number of cases that do not result in death.
QALYs Lost per Case
In estimating lost QALYs due to ABOM, we considered one possibility: the patient is ill for a defined period of time and then returns to full health. For more severe conditions, it would be appropriate to also consider the possibility of the patient dying; however, ABOM is not associated with significant mortality, and deaths are therefore unaddressed in the literature (see, for example, Huang, et al., 2011). We also consulted the Compressed Mortality File from the Centers for Disease Control and Prevention and the National Center for Health Statistics and found that the number of deaths associated with various types of acute otitis media were either zero or so small that they were labeled “unreliable.” Therefore, we do not consider the possibility of death in our calculations of QALYs or other social cost estimations for ABOM.
Assuming that all patients eventually recover from ABOM, we considered two possible scenarios: 1) the patient with ABOM is treated, and the initial treatment is successful, and 2) the patient with ABOM is treated, and the initial treatment is unsuccessful, delaying recovery. In the Tufts database, we located a paper that provided numbers of days spent in each stage of the illness/treatment, as well as associated QALY weights (Coco, 2007). This paper evaluated the patient condition over a standard of 30 days. Successful treatment resulted in the patient experiencing acute symptoms for 2.7 days, followed by 27 days of recuperation. Patients whose initial treatment was unsuccessful experienced the same acute symptoms for 2.7 days, followed by another 7 days when the patient would be even sicker; this leaves a 20 day recuperation period. The lost QALY calculations for both possibilities are shown below in Table 17.
According to the ABOM clinical practice guidelines, initial antibacterial drug therapy leads to symptomatic relief at 2 to 3 days in 91 percent of cases; therefore, we weighted success and failure possibilities at .91 and .09, respectively, to arrive at a weighted average of 0.00493 lost QALYs per ABOM episode (American Academy of Pediatrics and American Academy of Family Physicians, Subcommittee on Management of Acute Otitis Media, 2004).
Table 17: QALY Calculations for Acute Bacterial Otitis Media (ABOM)
|Scenario||Days of ABOM||Days of Treatment Success||Days of Treatment Failure|
|Initial Treatment Success (3)||QALY weight: 0.79
|QALY weight: 0.96
|Initial Treatment Failure (4)||QALY weight: 0.79
|QALY weight: 0.96
|QALY weight: 0.72
Source: Coco, Cost-Effectiveness Analysis of Treatment Options for Acute Otitis Media, 2007.
Total QALYs Lost due to Morbidity
Given that lost QALYs per ABOM case is 0.00493 and the total number of ABOM cases in the US is around 13.2 million, we computed the total annual QALYs lost due to ABOM morbidity to be around 65,000 (= 0.00493 × 13.2 million) in the US.
To calculate VSLY-based illness costs (for patients who do not die, which we assume to be all ABOM patients), we first calculated an average VSLY weighted by ABOM incidence by age group in 2011. This weighted average VSLY is roughly $228,000, which is then multiplied by the average lost QALYs per patient (0.00493) to arrive at $1,124 per patient which yields a total morbidity cost of $14.8 billion.