Journal of Infection (2012) 64, 445e447

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LETTER TO THE EDITOR

Greatly increased risk for prostatic abscess followingpyogenic liver abscess: A nationwide population-basedstudy

Dear Editor

We read the article by Chung et al.1 with great interest.The incidence of extra-hepatic metastases from pyogenicliver abscess (PLA) has also increased over the last two de-cades, with the occurrence rising from 3 to 12% of allcases.2e7 Severe complications of PLA have been reportedworldwide including septic endogenous endophthalmitis,metastatic infections of the brain and lungs, and necrotiz-ing fasciitis.8e10 Some case reports have indicated thatmetastatic septic emboli arising from PLA may also contrib-ute to the development of prostatic abscess (PA).4,7,11 How-ever, data regarding the longitudinal risk for developing PAin patients with PLA are still lacking. Therefore, we exam-ined the risk of PA among patients with PLA in comparisonto a control population using a large-scale population-baseddatabase in Taiwan.

The data for this study were retrieved from Taiwan’sNational Health Insurance Research Database (NHIRD),which is derived from the Taiwan National Health Insur-ance program. This study included a study group anda comparison group. For the study group, we first identi-fied 8678 male patients who visited outpatient care cen-ters or were hospitalized with a principal diagnosis ofPLA (ICD-9-CM code 572.0) between 2006 and 2008. Theirfirst visits for PLA between 2006 and 2008 were designatedas their index dates. Thereafter, we excluded those pa-tients who had received a diagnosis of PLA prior to theirindex date (n Z 610) in order to include only newly onsetpatients. We additionally excluded patients who had a his-tory of cholangitis, common bile duct stones, pancreatitis,inflammatory bowel disease, or endophthalmitis prior totheir index dates (n Z 112). We also excluded patients<18 years old (n Z 78). Finally, we excluded patientswho had been diagnosed with PA within one year prior totheir index dates (n Z 3). Ultimately, our study group in-cluded 7875 patients with PLA. We randomly selected78,750 subjects from the NHIRD, with a ratio of 1:10,matched with the study group patients based on age groupand year of index date. We assigned their first ambulatory

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care visit occurring in the index year as their index date.We ensured that none of the selected comparison subjectshad been diagnosed with PA within one year prior to theirindex dates.

Each subject was individually tracked for one year fromtheir index date to identify those who had received a sub-sequent diagnosis of PA (ICD-9-CM code 601.2) during thefollow-up period. We used stratified Cox proportionalhazards regressions (stratified on age) to compute theone-year hazard of prostatic abscess following a diagnosisof PLA.

The results showed that Klebiella pneumoniae(K. pneumonia) (ICD-9-CM code 041.3) was the causative or-ganism among 73.2% of the patients with PLA in this study.We found that patients with PLA were more likely to havediabetes, liver cirrhosis, and alcohol abuse/alcohol depen-dence syndrome than patients without PLA (Table 1).Among the total 86,625 sample, 34 (0.039%) subjects hadPA during the one-year follow-up period; PA was foundamong 26 (0.330%) patients with PLA and 8 (0.010%) pa-tients without PLA (Table 2). The average time betweenthe index date and PA diagnosis for the sampled patientswho had PA during the follow-up period was 50.2 days (stan-dard deviation Z 87.9 days); this was 28.2 days and 117days for patients with and without PLA, respectively(p < 0.001). Among the patients with PLA, three out ofthe 26 PA cases had been diagnosed within seven days fol-lowing their index date. After adjusting for patient monthlyincome, geographic location, urbanization level, diabetes,liver cirrhosis, and alcohol abuse/alcohol dependence syn-drome, the HR for PA among patients with PLA was 28.85(95% CI Z 12.89e64.50) times that of patients withoutPLA. We further analyzed the etiology of PA cases in this in-vestigation and found K. pneumonia to be the causative or-ganism among 69.2% of the cases, but only 12.5% of thecomparison group.

PLA had been considered rare in the past, with previousreports showing an annual incidence rate of 2.3/100,000and 1.0/100,000 in Canada and Denmark, respectively.12,13

However, PLA is endemic in Taiwan with incidence rates(17.59/100,000) over 17 times higher than that of Denmark,and seven times higher than Canada.14 Since metastatic in-fections in liver abscesses due to K. pneumoniae have beendemonstrated to result in poor outcomes,2,4,5,11 a numberof studies conducted in Taiwan have aimed to better char-acterize the septic metastatic lesions arising from PLA.

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Table 1 Demographic characteristics and comorbid medical disorders for patients with pyogenic liver abscess and patients inthe comparison cohort, 2006e2008 (n Z 86,625).

Variable Patients with pyogenic liverabscess n Z 7875

Comparison patientsn Z 78,750

P value

Total No. Column % Total No. Column %

Age (years) 1.00018e39 1011 12.8 10,110 12.840e49 1388 17.6 13,880 17.650e59 1925 24.4 19,250 24.460e69 1485 18.9 14,850 18.970e79 1496 19.1 14,960 19.1>79 570 7.2 5700 7.2

Diabetes 3506 44.5 16,686 21.2 <0.001Liver cirrhosis 846 10.7 1280 1.6 <0.001Alcohol abuse/alcoholdependence syndrome

105 1.3 382 0.5 <0.001

Monthly income 0.148NT$0�15,840 3339 42.4 32,524 41.3NT$15,841e25,000 2730 34.7 27,641 35.1�NT$25,001 1806 22.9 18,585 23.6

Geographic region 0.544Northern 3444 43.7 34,650 44.0Central 1881 23.9 18,501 23.5Southern 2342 29.7 23,231 29.5Eastern 208 2.7 2268 3.0

Urbanization level <0.0011 2203 28.0 22,638 28.82 2117 26.9 22,440 28.53 1276 16.2 13,672 17.44 1241 15.7 11,116 14.15 1038 13.2 8884 11.3

Note: Urbanization levels in Taiwan are divided into five strata according to the study by Lin HC, Chao PZ, Lee HC. Sudden sensorineuralhearing loss increases the risk of stroke: a 5-year follow-up study. Stroke 2008;39(10):2744-8.

446 Letter to the Editor

During the past two decades, many cases of endophthalmi-tis, meningitis, lung abscess, and necrotizing fasciitis asso-ciated with PLA were reported in Taiwan.4,11,15 However,documented reports of this condition associated with PAare rare. As far as we know, our study is the first to reportthe frequency of PA following PLA utilizing a nationwidepopulation-based dataset. Furthermore, our data also sup-port the theory that PLA could play a pathogenic role in thedevelopment of a PA.

Table 2 Crude and adjusted hazard ratios for prostatic absceperiod starting from the index ambulatory care visit (n Z 86,625

Presence ofprostatic abscess

Total sample Comparison

No. (%) No. (%)

One-year Follow-up PeriodYes 34 (0.04) 8 (0.01)No 86,595 (99.96) 78,742 (99.99)

Notes: a and * indicate p < 0.001. Adjustments are made for patient’salcohol abuse/alcohol dependence syndrome.

Our findings are strengthened by the use of a represen-tative sample from a comprehensive national database.The large sample size allowed us to maintain sufficientpower to detect associations. Despite these advantages,our findings need to be interpreted with caution due toseveral limitations. First, the NHIRD consists of dischargediagnoses provided by attending physicians, with no stan-dardized criteria used to define cases. This lack of stan-dardization could leave room for bias due to case

ss among the sample patients during the one–year follow-up).

Patients with liver abscess

No. (%) Crude HR(95% CI)

Adjusteda HR(95% CI)

26 (0.33) 32.57*(14.74e71.97)

28.85*(12.89e64.50)7849 (99.67)

monthly income, geographic region, diabetes, liver cirrohosis, and

Letter to the Editor 447

misclassification. Second, our sample size was small.However, collecting a large sample size during a limitedstudy period is difficult on account of the combined rarityof both PLA and PA.

This study provides a clear picture of the associationbetween PLA and PA. We found PA to be a rare event withinthe first-year following a diagnosis with PLA. Nevertheless,the incidence and risk of developing PA were significantlyincreased among the population with recent PLA whencompared with the comparison population. Physiciansshould be alert to the possible development of PA inpatients treated for PLA.

Disclosure

No conflict or financial interest to declare.

Acknowledgement

This study is based in part on data from the National HealthInsurance Research Database provided by the Bureau ofNational Health Insurance, Department of Health, Taiwanand managed by the National Health Research Institutes.The interpretations and conclusions contained herein donot represent those of the Bureau of National HealthInsurance, Department of Health, or the National HealthResearch Institutes.

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Shiu-Dong Chunga

School of Health Care Administration, Taipei MedicalUniversity, 250 Wu-Hsing St., Taipei 110, Taiwan

Division of Urology, Department of Surgery, Far EasternMemorial Hospital, Ban Ciao, Taipei, Taiwan

Graduate Institute of Clinical Medicine, College ofMedicine, National Taiwan University, Taipei, Taiwan

Joseph KellerDepartment of Urology, Taipei County Hospital,

Taipei, Taiwan

Herng-Ching Lin*School of Health Care Administration, Taipei Medical

University, 250 Wu-Hsing St., Taipei 110, TaiwanE-mail address: henry11111@tmu.edu.tw

Accepted 4 January 2012Available online 8 January 2012

* Corresponding author. Tel.: þ886 2 2736 1661x3613; fax: þ886 22378 9788.

a Dr. Shiu-Dong Chung is a Director at Department of Urology, FarEastern Memorial Hospital, Ban Ciao, Taipei, Taiwan. His researchinterests are epidemiology, prostatic abscess, and erectiledysfunction.