Clostridioides difficile infection, recurrence and the associated healthcare consumption in Sweden between 2006 and 2019: a population-based cohort study

BACKGROUND

Clostridioides difficile infection (CDI) causes a major burden to individuals and society, yet the impact may vary depending on age, sex, underlying comorbidities and where CDI was acquired (hospital or community).

METHODS

This Swedish nationwide population-based cohort study (2006-2019) compared all 43,150 individuals with CDI to their 355,172 matched controls (first year and entire follow-up). Negative binomial regression models compared the cumulated length of stay, number of in-hospital admissions, outpatient visits and prescriptions after the first CDI episode expressed as incidence rate ratios (IRR) and 95% confidence intervals for the entire follow-up.

RESULTS

Overall, 91.6% of CDI cases were hospital acquired, and 16.8% presented with recurrence(s); 74.8%of cases were ≥ 65 years and 54.2% were women. Compared to individuals without CDI, in-hospital stay rates were 18.01 times higher after CDI (95% CI 17.40-18.63, first-year: 27.4 versus 1.6 days), 9.45 times higher in-hospital admission (95% CI 9.16-9.76, first-year: 2.6 versus 1.3 hospitalisations), 3.94 times higher outpatient visit (95% CI 3.84-4.05, first-year: 4.0 versus 1.9 visits) and 3.39 times higher dispensed prescriptions rates (95% CI 3.31-3.48, first-year: 25.5 versus 13.7 prescriptions). For all outcomes, relative risks were higher among the younger (< 65 years) than the older (≥ 65 years), and in those with fewer comorbidities, but similar between sexes. Compared to those without recurrence, individuals with recurrence particularly showed a higher rate of hospital admissions (IRR = 1.18, 95% 1.12-1.24). Compared to community-acquired CDI, those with hospital-acquired CDI presented with a higher rate of hospital admissions (IRR = 7.29, 95% CI 6.68-7.96) and a longer length of stay (IRR = 7.64, 95% CI 7.07-8.26).

CONCLUSION

CDI was associated with increased health consumption in all affected patient groups. The majority of the CDI burden could be contributed to hospital-acquired CDI (~ 9/10), older patients (~ 3/4) and those with multiple comorbidities (~ 6/10 Charlson score ≥ 3), with 1/5 of the total CDI burden contributed to individuals with recurrence. Yet, relatively speaking the burden was higher among the younger and those with fewer comorbidities, compared to their peers without CDI.

The combined effect of systemic antibiotics and proton pump inhibitors on Clostridioides difficile infection and recurrence

BACKGROUND

Antibiotics and proton pump inhibitors (PPI) are recognized risk factors for acquisition and recurrence of Clostridioides difficile infection (CDI), yet combined effects remain unclear.

OBJECTIVES

To assess the short- and long-term effects of antibiotics and PPIs on CDI risk and recurrence.

METHODS

Population-based study including all 43 152 patients diagnosed with CDI in Sweden (2006-2019), and 355 172 matched population controls without CDI. The impact of antibiotics and PPIs on CDI risk and recurrence was explored for recent (0-30 days) and preceding (31-180 days) use prior to their first CDI diagnosis, using multivariable conditional logistic regression presented as odds ratios (ORs) and 95% confidence interval, adjusted for demographics, comorbidities and other drugs.

RESULTS

Compared to controls, the combined effect of recent PPIs and antibiotics [ORAB+PPI = 17.51 (17.48-17.53)] on CDI risk was stronger than the individual effects [ORAB = 15.37 (14.83-15.93); ORPPI = 2.65 (2.54-2.76)]. Results were less pronounced for exposure during the preceding months. Dose-response analyses showed increasing exposure correlated with CDI risk [recent use: ORAB = 6.32 (6.15-6.49); ORPPI = 1.65 (1.62-1.68) per prescription increase].Compared to individuals without recurrence (rCDI), recent [ORAB = 1.30 (1.23-1.38)] and preceding [ORAB = 1.23 (1.16-1.31); ORPPI = 1.12 (1.03-1.21)] use also affected the risk of recurrence yet without significant interaction between both. Recent macrolides/lincosamides/streptogramins; other antibacterials including nitroimidazole derivates; non-penicillin beta lactams and quinolones showed the strongest association with CDI risk and recurrence, particularly for recent use. PPI use, both recent and preceding, further increased the CDI risk associated with almost all antibiotic classes.

CONCLUSION

Recent and less recent use of PPIs and systemic antibiotics was associated with an increased risk of CDI, particularly in combination.

Clostridioides difficile infection-associated cause-specific and all-cause mortality: A population-based cohort study

OBJECTIVES

Clostridioides difficile infection (CDI) is a common healthcare-associated infection and leading cause of gastroenteritis-related mortality worldwide. However, data on CDI-associated mortality are scarce. We aimed to examine the association between CDI and all-cause and cause-specific mortality. We additionally explored contributing causes of mortality, including recurrent CDI (rCDI), hospital- or community-acquired CDI, chronic comorbidities, and age.

METHODS

This nationwide population-based cohort study (from 2006-2019) compared individuals with CDI to the entire Swedish background population using standardized mortality ratios (SMRs). Additionally, a matched cohort design (1:10), utilizing multivariable Poisson regression models, provided incidence rate ratios (IRRs) with 95% confidence intervals (CIs).

RESULTS

This study included 43,150 individuals with CDI and 355,172 controls. In total, 69.7% were ≥65 years, and 54.9% were female. CDI was associated with a 3- to 7-fold increased mortality rate (IRR=3.5, 95% CI: 3.3-3.6; SMR=6.8, 95% CI:6.7-6.9) compared to the matched controls and Swedish background population, respectively. Mortality rates were highest for hospital-acquired CDI (IRR=2.4, 95% CI: 1.9-3.2) and during the first CDI episode (IRR=0. 2, 95% CI: 0.2-0.3 for recurrent versus first CDI). Individuals with CDI had more chronic comorbidities than controls, yet mortality remained higher among CDI cases even after adjustment and stratification for comorbidity; CDI was associated with increased mortality (IRR=6.1, 95% CI: 5.5-6.8), particularly among those without any chronic comorbidities.

CONCLUSIONS

CDI was associated with elevated all-cause and cause-specific mortality, despite possible confounding by ill health. Mortality rates were consistently increased across both sexes, all age groups, and comorbidity groups.

Maternal and Early-Life Exposure to Antibiotics and the Risk of Autism and Attention-Deficit Hyperactivity Disorder in Childhood: a Swedish Population-Based Cohort Study

INTRODUCTION

Antibiotics represent the most common type of medication used during pregnancy and infancy. Antibiotics have been proposed as a possible factor in changes in microbiota composition, which may play a role in the aetiology of autism and attention deficit/hyperactivity disorder (ADHD). Our aim was to investigate the association between maternal and early-life antibiotic use and autism and ADHD in childhood.

METHODS

This Swedish nation-wide population-based cohort study included all first live singleton births (N = 483,459) between January 2006 and December 2016. The association of dispensed antibiotics with autism and ADHD in children aged ≤ 11 years was estimated by applying multivariable logistic regression and generalised estimating equations models.

RESULTS

Of the mothers, 25.9% (n = 125,106) were dispensed ≥1 antibiotic during the exposure period (from 3 months pre-conception to delivery), and 41.6% (n = 201,040) of the children received ≥ 1 antibiotic in early life (aged ≤ 2 years). Penicillin was the most prescribed antibiotic class (17.9% of mothers, 38.2% of children). Maternal antibiotic use was associated with an increased risk of autism [odds ratio (OR) = 1.16, 95% confidence interval (CI) 1.09-1.23] and ADHD (OR = 1.29, 95% CI 1.21-1.36) in childhood. Early-life exposure to antibiotics showed an even stronger association [autism (OR = 1.46, 95% CI 1.38-1.55); ADHD (OR = 1.90, 95% CI 1.80-2.00)]. Both maternal and childhood-exposure sub-analyses suggested a dose-response relationship.

CONCLUSION

Maternal and early-life antibiotic use was associated with an increased risk of autism and ADHD in childhood. However, differences were noted by exposure period and antibiotic classes.

Maintenance Proton Pump Inhibitor Use Associated with Increased All-Cause and Cause-Specific Mortality in Sweden

BACKGROUND

Proton pump inhibitor (PPI) use has increased over the last decades and has been associated with multiple adverse events and potentially even overall survival.

AIMS

We aimed to investigate the association between proton pump inhibitor maintenance use and all-cause and cause-specific mortality, addressing confounding by indication and duration of use.

METHODS

This Swedish population-based cohort study included all adult (N = 935,236) PPI and histamine-2 receptor antagonist maintenance users (≥ 180 days use) during 2005-2014. Standardised mortality ratios (SMRs) and 95% confidence intervals were calculated for all-cause and cause-specific mortality comparing the risk among PPI/H2RA users to that of the Swedish background population, stratified by age, sex, calendar period, indication and duration of use. Multivariable Poisson regression models were used to compare PPI use to H2RA use, expressed as incidence rate ratios and 95% confidence intervals.

RESULTS

PPI and histamine-2 receptor antagonist use were associated with an increased risk of all-cause mortality (SMR = 1.35; 1.34-1.36; SMR = 1.31; 1.27-1.36, respectively). The highest SMRs were found in the youngest age groups. In direct comparison, PPI use showed a higher mortality risk than histamine-2 receptor antagonist use (incidence rate ratios = 1.42; 1.38-1.46). PPIs were related to increased cancer (SMR = 1.21; 1.20-1.22), and cardiovascular mortality (SMR = 1.36; 1.35-1.37). Increased SMRs were observed for most indications. Longer duration of use was associated with a higher mortality among PPI users but not among histamine-2 receptor antagonist users.

CONCLUSION

Maintenance PPI use was associated with an increased risk of all-cause and cause-specific mortality, and the risk increased with prolonged duration.

Population-based cohort study: proton pump inhibitor use during pregnancy in Sweden and the risk of maternal and neonatal adverse events

BACKGROUND

Approximately half of all women suffer from heartburn at some stage during pregnancy. The most effective treatment is proton pump inhibitors, but the safety of use during pregnancy cannot be guaranteed. This study aimed to elucidate the effect of proton pump inhibitors on the risk of pre-eclampsia, gestational diabetes mellitus, preterm birth, an Apgar score at 5 min below 7, and a child being small or large for its gestational age.

METHODS

This Swedish population-based study included 1,089,514 live singleton deliveries between July 2006 and December 2016 in Sweden. Multiple logistic regression was used to model the outcomes as a function of the covariates. Results were presented as odds ratios with 95% confidence intervals.

RESULTS

In 1.4% of all pregnancies, the mother used proton pump inhibitors in the period from 3 months before the last menstrual period up to delivery. The use of proton pump inhibitors was associated with higher odds of pre-eclampsia (odds ratio = 1.19, 1.10-1.29), gestational diabetes mellitus (odds ratio = 1.29, 1.16-1.43), preterm birth (odds ratio = 1.23, 1.14-1.32), and small for gestational age (odds ratio = 1.27, 1.16-1.40) and lower odds of large for gestational age (odds ratio = 0.84, 0.77-0.91). No significant association was found with a low Apgar score 5 min after birth.

CONCLUSIONS

Proton pump inhibitor use was associated with a higher risk of pre-eclampsia, gestational diabetes, preterm birth, and being born small for gestational age.

Association between menopausal hormone therapy use and mortality risk: a Swedish population-based matched cohort study

BACKGROUND

The net effect of menopausal hormone therapy on the risk of death is understudied, and current evidence is conflicting. Our aim was to investigate the association between menopausal hormones and risk of all-cause, cardiovascular, and cancer-specific mortality, based on the Swedish Prescribed Drug Registry and National Patient Registry.

METHODS

This Swedish population-based matched cohort study included all women, 40 years or older, who had received at least one prescription of systemic menopausal hormone therapy between 2005-2014 (n = 290,186), group level matched 1:3 to non-users (n = 870,165). Multivariable conditional logistic regression models estimated the relative risk of all-cause and cause-specific mortality, adjusting for several clinical factors and comorbidities.

RESULTS

Ever-use of menopausal hormones was associated with a slightly lower overall odds of all-cause (OR = 0.97, 95%CI 0.95-0.98) and cardiovascular (OR = 0.97, 95%CI 0.95-0.99) mortality, whilst 30% lower overall odds of cancer-related mortality (OR = 0.70, 95%CI 0.68-0.72) was shown. The odds of all-cause and cancer-related mortality were consistently reduced among women who began menopausal hormone therapy ≤60 years, whereas the association with cardiovascular mortality was inconsistent. In contrast, oestrogen-only therapy was associated with elevated odds of all-cause (OR = 1.14, 95%CI 1.11-1.16) and cardiovascular mortality (OR = 1.04, 95%CI 1.01-1.06) among women who began treatment at ≥70 years. Among current users, oestrogen-only therapy was associated with higher odds of all-cause (OR = 1.48, 95%CI 1.44-1.52) and cardiovascular mortality (OR = 1.24, 95%CI 1.20-1.28), whereas past use of oestrogen-only therapy suggested lower odds of mortality.

CONCLUSIONS

Our generalisable data suggest that early menopausal hormone treatment initiation does not increase the odds of mortality. However, the role of oestrogens in particularly cardiovascular mortality remains to be investigated.

Pregnancy, perinatal and childhood outcomes in women with and without polycystic ovary syndrome and metformin during pregnancy: a nationwide population-based study

BACKGROUND

Polycystic Ovary Syndrome (PCOS) is an endocrine disorder that affects women in reproductive age and represents an unfavourable risk factor for several pregnancy and perinatal outcomes. Despite, no guidelines or pharmaceutical strategies for treating PCOS during pregnancy are available. The aim of this study is to determine the association between polycystic ovary syndrome with or without metformin and the pregnancy, perinatal outcomes as well as the risk of obesity in children born to these mothers.

METHODS

In this nationwide population-based cohort study based in Swedish population, all singleton births (n = 1,016,805) from 686,847 women since 2006 up to 2016 were included. Multivariable logistic and Cox regression modelling with odds ratios (OR) and hazard ratios (HR) and 95% confidence intervals were used to study the association between the exposure of maternal PCOS, metformin during pregnancy (or the combination of both) and: 1) Pregnancy outcomes: preeclampsia, gestational diabetes, caesarean section, and acute caesarean section, 2) Perinatal outcomes: preterm birth, stillbirth, low birth weight, macrosomia, Apgar < 7 at 5 min, small for gestational age and large for gestational age, and 3) Childhood Obesity.

RESULTS

PCOS in women without metformin use during pregnancy was associated with higher risks of preeclampsia (OR = 1.09, 1.02-1.17), gestational diabetes (OR = 1.71, 1.53-1.91) and caesarean section (OR = 1.08, 1.04-1.12), preterm birth (OR = 1.30, 1.23-1.38), low birth weight (OR = 1.29, 1.20-1.38), low Apgar scores (OR = 1.17, 1.05-1.31) and large for gestational age (OR = 1.11, 1.03-1.20). Metformin use during pregnancy (in women without PCOS) was associated with a 29% lower risks of preeclampsia (OR = 0.71, 0.51-0.97), macrosomia and large for gestational age. Obesity was more common among children born to mothers with PCOS without metformin (HR = 1.61, 1.44-1.81); and those with metformin without PCOS (HR = 1.67, 1.05-2.65). PCOS with metformin was not associated with any adverse outcome.

CONCLUSION

PCOS was associated with increased risks of adverse pregnancy and perinatal outcomes and childhood obesity. Metformin appears to reduce these risks in mothers with polycystic ovary syndrome and their children; but may increase the risk of childhood-obesity in children form women without PCOS.

Risk of hepatocellular carcinoma in hepatitis B and D virus co-infected patients: A systematic review and meta-analysis of longitudinal studies

Hepatitis D virus (HDV) infection causes a severe chronic viral hepatitis with accelerated development of liver cirrhosis and decompensation, but whether it further increases the risk of hepatocellular carcinoma (HCC) is unclear. We performed a comprehensive systematic review of the published literature and meta-analysis to assess the risk of HCC in HDV and hepatitis B virus (HBV) co-infected, compared to HBV mono-infected patients. The study was conducted per a priori defined protocol, including only longitudinal studies, thus excluding cross-sectional studies. Random-effects models were used to determine aggregate effect sizes (ES) with 95% confidence intervals (CI). Meta-regression was used to examine the associations among study level characteristics. Twelve cohort studies comprising a total of 6099 HBV/HDV co-infected and 57,620 chronic HBV mono-infected patients were analysed. The overall pooled ES showed that HBV/HDV co-infected patients were at 2-fold increased risk of HCC compared to HBV mono-infected patients (ES = 2.12, 95% CI 1.14-3.95, I²  = 72%, N = 12). A six-fold significant increased risk of HCC was noted among HIV/HBV/HDV triple-infected, compared to HIV/HBV co-infected patients. The magnitude of ES did not differ significantly after adjustment for study design and quality, publication year and follow-up duration in univariable meta-regression analysis. This systematic review and meta-analysis shows that infection with HDV is associated with a 2-fold higher risk of HCC development compared to HBV mono-infection. HCC surveillance strategies taking this increased risk into account, and new treatment options against HDV, are warranted.

Prediagnostic use of estrogen-only therapy is associated with improved colorectal cancer survival in menopausal women: a Swedish population-based cohort study

BACKGROUND

Menopausal hormone therapy (MHT) reduces the risk of developing colorectal cancer (CRC), yet it is largely unclear whether it could also influence survival in women with CRC. Therefore, we aimed to investigate the influence of prediagnostic MHT use on CRC-specific and all-cause mortality in women with CRC.

METHODS

This nationwide nested cohort study, within a large population-based matched cohort, included all women diagnosed with incident CRC between January 2006 and December 2012 (N = 7814). A total of 1529 women had received at least one dispensed prescription of systemic MHT before CRC diagnosis, and 6285 CRC women with CRC did not receive MHT during the study period, as ascertained from the Swedish Prescribed Drug Registry. Multivariable Cox regression models provided adjusted hazard ratios (HRs) with 95% confidence intervals (CIs) for CRC-specific mortality and all-cause mortality.

RESULTS

Past use of prediagnostic estrogen-only therapy (E-MHT) was associated with lower CRC-specific (HR = 0.67, 95%CI 0.44-0.99) and all-cause mortality (HR = 0.68, 95%CI 0.59-0.93). However, all-cause mortality (HR = 1.23, 95%CI 1.02-1.48) was elevated among current prediagnostic E-MHT users who were 70+ years at diagnosis. Current estrogen combined progestin therapy (EP-MHT) was associated with higher CRC-specific mortality (HR = 1.61, 95%CI 1.06-2.44) in older women, but no association was shown for all-cause mortality.

CONCLUSIONS

Our findings suggest that E-MHT, but not EP-MHT use, might be associated with improved CRC survival, indicating a potential role of estrogens in sex hormone-related cancers. However, association of MHT use with grade of cancer remains unclear.

Menopausal hormone therapies and risk of colorectal cancer: a Swedish matched-cohort study

BACKGROUND

Menopausal hormone therapy (MHT) has been associated with various malignancies.

AIMS

To investigate the association of various MHT regimens with the risk of colorectal cancer (CRC).

METHODS

All MHT ever-users (n = 290 186) were included through the Swedish Prescribed Drug Registry, with a 1:3 group-level matching to non-users. Ever-users were defined as women who received ≥1 dispensed prescription of systemic MHT during 2005-2012 in Sweden. All CRC cases after drug initiation were extracted from the Swedish Cancer Registry. The association was assessed by multivariable conditional logistic and Cox regression models, presented as odds ratios (ORs) or hazard ratios (HRs) with 95% confidence intervals (CIs) considering different regimens, duration and age at treatment initiation.

RESULTS

Compared with non-users, MHT users had an overall reduced odds for colon (OR = 0.67, 95% CI 0.63-0.72) and rectal adenocarcinoma (OR = 0.66, 95% CI 0.60-0.73), especially among women aged 40-60 years. Current users of oestrogen-only preparations (E-MHT) showed a reduced odds (colon OR = 0.73, 95% CI 0.65-0.82; rectal OR = 0.76, 95% CI 0.64-0.90) compared to non-users, particularly with oestradiol and oestriol. Past E-MHT use showed stronger odds reductions (colon OR = 0.49, 95% CI 0.43-0.56; rectal OR = 0.36, 95% CI 0.28-0.45). Current use of oestrogen combined progestin therapy (EP-MHT) indicated a less prominent odds reduction (colon adenocarcinoma OR 0.62, 95% CI 0.54-0.72; rectal adenocarcinoma OR = 0.60, 95% CI 0.49-0.74) than past users. Tibolone showed an increased risk of left-sided colorectal adenocarcinoma. Oral and cutaneous MHT usage showed similar patterns.

CONCLUSIONS

MHT use may decrease colorectal adenocarcinoma risk, for both E-MHT and EP-MHT, and especially in past users.

Antibiotic use and risk of colorectal cancer: a systematic review and dose-response meta-analysis

BACKGROUND

It is understudied whether the posed association of oral antibiotics with colorectal cancer (CRC) varies between antibiotic spectrums, colorectal continuum, and if a non-linear dose-dependent relationship is present.

DESIGN

Three electronic databases and a trial platform were searched for all relevant studies, from inception until February 2020, without restrictions. Random-effects meta-analyses provided pooled effect-sizes (ES) with 95% confidence intervals (CI). Dose-response analyses modelling the relationship between number of days exposed to antibiotics and CRC risk were extended to non-linear multivariable random-effects models.

RESULTS

Of 6483 identified publications ten were eligible, including 4.1 million individuals and over 73,550 CRC cases. The pooled CRC risk was increased among individuals who ever-used antibiotics (ES = 1.17, 95%CI 1.05-1.30), particularly for broad-spectrum antibiotics (ES = 1.70, 95%CI 1.26-2.30), but not for narrow-spectrum antibiotic (ES = 1.11, 95% 0.93-1.32). The dose-response analysis did not provide strong evidence of any particular dose-response association, and the risk patterns were rather similar for colon and rectal cancer.

DISCUSSION

The antibiotic use associated CRC risk seemingly differs between broad- and narrow-spectrum antibiotics, and possibly within the colorectal continuum. It remains unclear whether this association is causal, requiring more mechanistic studies and further clarification of drug-microbiome interactions.

Antibiotic use and the risk of breast cancer: A systematic review and dose-response meta-analysis

OBJECTIVE

Oral antibiotics are posed as a possible risk factor for breast cancer. Evidence is insufficient to determine whether the choice of antibiotic class could effect this potential association, and non-linearity has not been studied. We aimed to fill these important knowledge gaps.

METHODS

PubMed, Web of Science, Embase and a trial registry were searched from inception until January 2020, without any restrictions. Additionally, extensive manual searches were undertaken. Random-effects meta-analyses provided pooled risk estimates with 95 % confidence intervals (CI). Dose-response analyses modeling the relationship between number of antibiotic prescriptions and breast cancer risk were extended to non-linear models. Heterogeneity, publication bias and small-study effects were assessed.

RESULTS

Of 7805 identified publications ten were eligible, including 3,719,383 individuals and 84,485 breast cancer cases. The pooled breast cancer risk was modestly increased among individuals who ever used antibiotics (relative risk RR = 1.18, 95 %CI 1.08-1.29), also after excluding the last year prior diagnosis. This excess risk was seen among penicillin (RR = 1.09, 95 %CI 1.01-1.18), tetracycline (RR = 1.13, 95 %CI 1.04-1.24) and nitrofuran users (RR = 1.26, 95 %CI 1.05-1.52), whilst nitroimidazole and metronidazole use (RR = 1.05, 95 %CI 1.00-1.11) indicated for marginal association. No apparent association was found for other antibiotics. Data suggested for a non-linear dose-dependent relationship, with a seemingly protective effect after at least 35 prescriptions. However, these findings might partly be explained by limited power of dose-response analyses.

CONCLUSIONS

The association of antibiotics with breast cancer risk appears to differ between the various antibiotic classes. Whether this association is causal remains unclear, requiring further clarification and mechanistic studies.

Menopausal hormone therapy treatment options and ovarian cancer risk: A Swedish prospective population-based matched-cohort study

Although menopausal hormone therapy (MHT) seemingly increases the risk of ovarian cancer, evidence is insufficient whether the risk varies between various MHT formulations, regimens and administration modes. With the aim of filling these knowledge gaps, we investigated the effect of different MHT treatment options on the risk of ovarian cancer. This prospective Swedish population-based matched-cohort study included all women ≥40 years having used systemic MHT between 2005 and 2012 (288,950 ever-users), group-level matched (1:3) to 866,546 nonusers. MHT use was ascertained from the Swedish Prescribed Drug Registry and data was linked to several national health data registries. Multivariable conditional logistic regression provided odds ratios (ORs) and 95% confidence intervals (CIs) adjusted for parity, and comorbidities. Current EP-MHT use was associated with a modestly increased risk of ovarian cancer (OR = 1.38, 95% CI 1.18-1.62), while no consistent risk was found among past users (OR = 1.00, 95% CI 0.84-1.18). Current continuous testosterone derived (OR = 1.50, 95% CI 1.15-1.96) regimens increased the risk whereas progesterone derived (OR = 1.48, 95% CI 1.00-2.21) regimens increased the risk marginally. Nonsignificant positive associations were observed for sequential regimens (OR = 1.87, 95% CI 0.70-5.08; OR = 1.54, 95% CI 0.96-2.47, respectively). An inverse relationship was observed for all E-MHT use (OR = 0.25, 95% CI 0.22-0.29), but this association might partly be explained by underreporting of oophorectomies or tubal ligations. Current cutaneous EP-MHT (OR = 1.28, 95% CI 0.81-2.02) suggested a possibly lower risk than oral MHT (OR = 1.48, 95% CI 1.25-1.75). In conclusion EP-MHT, notably continuous regimens, were associated with a modestly increased risk of ovarian cancer. The role of E-MHT requires further clarification.