Comparative analysis of within-host diversity among vaccinated COVID-19 patients infected with different SARS-CoV-2 variants.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a rapidly evolving RNA virus that mutates within hosts and exists as viral quasispecies. Here, we evaluated the within-host diversity among vaccinated and unvaccinated individuals (n = 379) infected with different SARS-CoV-2 Variants of Concern. The majority of samples harbored less than 14 intra-host single-nucleotide variants (iSNVs). A deep analysis revealed a significantly higher intra-host diversity in Omicron samples than in other variants (p value < 0.05). Vaccination status and type had a limited impact on intra-host diversity except for Beta-B.1.315 and Delta-B.1.617.2 vaccinees, who exhibited higher diversity than unvaccinated individuals (p values: <0.0001 and <0.0021, respectively). Three immune-escape mutations were identified: S255F in Delta and R346K and T376A in Omicron-B.1.1.529. The latter 2 mutations were fixed in BA.1 and BA.2 genomes, respectively. Overall, the relatively higher intra-host diversity among vaccinated individuals and the detection of immune-escape mutations, despite being rare, suggest a potential vaccine-induced immune pressure in vaccinated individuals.

Common Indications for Referral to the Healthcare system for COVID-19 recovered patients versus Qatar Biobank study population: A descriptive analysis.

BACKGROUND AND AIM OF THE WORK: Qatar Biobank (QBB) is actively acquiring data on the range of short- and long-term health impacts associated with COVID-19. This is performed through the COVID-19 biorepository National project. In this report, we describe the most common indications for the referral to Qatar's healthcare system of COVID-19 biorepository participants in comparison with the Qatar Biobank (QBB) general population study. Methods Patients with a laboratory diagnosis of COVID-19, who were Qatar residents that could communicate in Arabic, English, Hindi and Urdu were eligible to participate in the COVID-19 biorepository project. Biological samples of Consented participants were collected on a weekly basis until recovery, and then monthly for a year. Participants were also offered a bone density scan three months after recovery and non-contrast MRI brain and whole-body scan six months after recovery. Number of participants requiring referral for medical follow up after recovery for any abnormal clinically significant findings were recorded and statistically compared to general population referred participants Results: The majority of referrals for the general population study was for osteopenia versus diabetes for the COVID-19 biorepository project Conclusion Descriptive analysis of the referral data of the COVID-19 participants and QBB general population (not previously affected by the virus) shows a clear difference between the two populations' reasons for referrals. Diabetes for COVID 19 recovered participants versus osteopenia for general population Keywords: COVID19, Reason for Referrals, Diabetes, Qatar biobank.

The prevalence of HEV among non-A-C hepatitis in Qatar and efficiency of serological markers for the diagnosis of hepatitis E.

BACKGROUND: The rapid growth of Qatar in the last two decades has attracted a large influx of immigrant workers who mostly come from HEV-hyperendemic countries. Thus, we aim to investigate the prevalence of HEV among acute non-A-C hepatitis patients in Qatar; and to evaluate the performance of four dominant commercial serological assays for HEV diagnosis. METHODS: 259 patients with non-A-C hepatitis were tested using the Wantai HEV-IgM, HEV-IgG, HEV-Ag ELISA kits, and the MP Biomedical HEV-Total Ab ELISA kit. ALT levels were tested and HEV RNA (viral loads) was performed using Taqman AmpliCube HEV RT-PCR kit (Mikrogen, Neuried, Germany). The performance of each kit was assessed according to the RT-PCR results. RESULTS: HEV-RNA was detected in 23.1% of the samples. Most of these HEV-RNA-positive cases belonged to non-Qatari residents from the Indian subcontinent; India, Pakistan, etc. HEV-Ag, HEV-IgM, HEV-IgG, HEV-Total Ab were detected in 5.56%, 8.65%, 32.1%, and 34.2% of all tested samples, respectively. Elevated ALT levels were highly correlated with the HEV-Ag, HEV-IgM, HEV-RNA but not with the HEV-IgG and HEV-Total Ab. Although HEV-Ag was very specific (100%), yet its sensitivity was poor (36.7%). HEV-IgM demonstrated the best second marker for diagnosis of acute HEV after RT-PCR as jugged by the overall performance parameters: specificity (96.2%), sensitivity (71.4%), PPV (83.3%), NPP (92.7%), agreement with RT-PCR (91.0%), and Kappa-value (0.71). CONCLUSION: Our study demonstrated a high prevalence of HEV virus in Qatar, mostly among immigrants from the Indian subcontinent. The HEV-IgM represents the best marker for detecting the acute HEV infection, where RT-PCR cannot be performed.

Failure to replicate the association of rare loss-of-function variants in type I IFN immunity genes with severe COVID-19.

A recent report found that rare predicted loss-of-function (pLOF) variants across 13 candidate genes in TLR3- and IRF7-dependent type I IFN pathways explain up to 3.5% of severe COVID-19 cases. We performed whole-exome or whole-genome sequencing of 1,934 COVID-19 cases (713 with severe and 1,221 with mild disease) and 15,251 ancestry-matched population controls across four independent COVID-19 biobanks. We then tested if rare pLOF variants in these 13 genes were associated with severe COVID-19. We identified only one rare pLOF mutation across these genes amongst 713 cases with severe COVID-19 and observed no enrichment of pLOFs in severe cases compared to population controls or mild COVID-19 cases. We find no evidence of association of rare loss-of-function variants in the proposed 13 candidate genes with severe COVID-19 outcomes.

Conception, Implementation, and Integration of Heterogenous Information Technology Infrastructures in the Qatar Biobank.

The overall goal of the Qatar Biobank (QBB) is to collect, manage, and distribute high-quality human biospecimens with appropriate clinical and/or research annotation and associated phenotypic data, aiming to be an important and essential resource of medical research and evidence-based health care system policies in Qatar. To manage and collect large volumes of data, the QBB has been investing in a number of information management solutions, trying to avoid inflexibility of traditional systems and accommodate changes in data sources and workflows. This article aims to present the information technology solutions of QBB based on a free, open-source software solution, considered a reliable alternative to commercial solutions. After evaluating the free, open-source software solutions available for biobanks, Onyx from ObiBa was utilized to develop custom components to interface various clinical devices, LIMS and Picture Archiving and Communication System, which has varying integration capabilities. This is a showcase for biobanks to carefully evaluate and select hardware and software to automate their operations providing the functions required for business continuity.

Qatar Biobank: A Paradigm of Translating Biobank Science into Evidence-Based Health Care Interventions.

Biobank science is progressively becoming indispensable for the development of novel diagnostic tools in health care, by pairing standardized high-quality biological samples, phenotypic, and omics data required to best characterize the underlying biological mechanisms of response to therapy and survival. Qatar Biobank (QBB), Qatar's National Repository Centre for biological samples and health information, aligning with these endeavors, has developed a strategic framework to enable biobanking science that can be transformed into tangible health care diagnostic tools. In this concept, QBB works closely with multidisciplinary stakeholders: (1) governmental authorities (n = 2), (2) health providers (n = 3), (3) academic institutions (n = 28), (4) other research institutions (n = 6), and (5) the Qatar National Research Fund, by providing data and biospecimens to research projects. The local community organizes campaigns through social media and interactive events, spreading the concept of biobanking to inform and encourage people to participate. Up to now, QBB has recruited up to 30% of the targeted population and collaborated with 35 national and international research entities contributing to more than 170 research projects. QBB is referring about 53% of its participants to the Hamad general hospital through the integrated information system, revealing the need of new health screening approaches for public health policy makers. QBB contributed to the development of a customized genetic screening microarray tailored to the Qatari population that will be used in research as well as for the screening of variants of medical relevance in Qatar, promoting precision medicine in Qatar's health care system. The QBB strategic plan is a paradigm for the optimal utilization of resources, infrastructure, and investments engaging the local authorities and the research entities, and committing them to data sharing and working together toward the discovery of evidence-based health care interventions.

Qatar Biobank Cohort Study: Study Design and First Results.

We describe the design, implementation, and results of the Qatar Biobank (QBB) cohort study for the first 10,000 participants. QBB is a prospective, population-based cohort study in Qatar, established in 2012. QBB's primary goal was to establish a cohort accessible to the local and international scientific community, providing adequate health data and biological samples to enable evidence-based research. The study design is based on an agnostic hypothesis, collecting data using questionnaires, biological samples, imaging data, and -omics. QBB aims to recruit 60,000 participants, men and women, adult (aged ≥18 years) Qataris or long-term residents (≥15 years living in Qatar) and follow up with them every 5 years. Currently, QBB has reached 28% (n = 17,065) of the targeted enrollee population and more than 2 million biological samples. QBB is a multinational cohort including 33 different nationalities, with a relatively young population (mean age, 40.5 years) of persons who are highly educated (50% university-educated) and have high monthly incomes. The 4 main noncommunicable diseases found among the QBB population are dyslipidemia, diabetes, hypertension, and asthma with prevalences of 30.1%, 17.4%, 16.8%, and 9.1%, respectively. The QBB repository can provide data and biological samples sufficient to demonstrate valid associations between genetic and/or environmental exposure and disease development to scientists worldwide.

Antibacterial Properties of Polysulfone Membranes Blended with Arabic Gum.

Polysulfone (PS) membranes blended with different loadings of arabic gum (AG) were synthesized using phase inversion method and the antibacterial properties of the synthesized membranes were tested using a number Gram-negative (Escherichia coli, Klebsiella pneumonia and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus) bacterial species. It was shown that AG addition to the dope polymer solutions essentially changed porous structure, hydrophilicity and zeta potential of the cast PS/AG membranes. These changes were due to the amphiphilic properties of AG macromolecules that contained negatively charged hydrophilic residues. A pronounced decrease in bacterial attachment was seen in the field emission scanning electron microscopy (FESEM) images for PS/AG membrane samples compared to both commercial (Microdyn-Nadir) and bare PS (without AG) membranes. AG loading dependent trend was observed where the prevention of bacterial colonization on the membrane surface was strongest at the highest (7 wt. %) AG loading in the casting solution. Possible mechanisms for the prevention of bacterial colonization were discussed. Significantly, the inhibition of bacterial attachment and growth on PS/AG membranes was observed for both Gram-positive and Gram-negative bacterial models, rendering these novel membranes with strong biofouling resistance attractive for water treatment applications.

Molecular Analysis of the Enteric Protozoa Associated with Acute Diarrhea in Hospitalized Children.

Pediatric diarrhea is a common cause of death among children under 5 years of age. In the current study, we investigated the frequency of intestinal parasites among 580 pediatric patients with chronic diarrhea. Parasitic protozoa (all species combined) were detected by molecular tools in 22.9% of the children and the most common parasite was Cryptosporidium spp. (15.1%). Blastocystis hominis was detected in 4.7%, Dientamoeba fragilis in 4%, Giardia duodenalis in 1.7%, and Entamoeba histolytica in 0.17%. Protozoan infections were observed among all regional groups, but prevalence was highest among Qatari subjects and during the winter season. Typing of Cryptosporidium spp. revealed a predominance of Cryptosporidium parvum in 92% of cases with mostly the IIdA20G1 subtype. Subtypes IIdA19G2, IIdA18G2, IIdA18G1, IIdA17G1, IIdA16G1, and IIdA14G1 were also detected. For Cryptosporidium hominis, IbA10G2 and IbA9G3 subtypes were identified. This study provides supplementary information for implementing prevention and control strategies to reduce the burden of these pediatric protozoan infections. Further analyses are required to better understand the local epidemiology and transmission of Cryptosporidium spp. in Qatar.

Human Papillomavirus (HPV) Infection: Molecular Epidemiology, Genotyping, Seroprevalence and Associated Risk Factors among Arab Women in Qatar.

Human Papillomavirus (HPV) infections are known to cause cervical cancer worldwide, however, limited information is currently available on prevalence, types distribution and risk factors for HPV infection in the Arab countries. We conducted a cross-sectional observational study exclusively of women of Arabic origin residing in Qatar (n = 406) who were selected from the Women's Hospital at Hamad Medical Corporation (HMC) and Health Centers of the Primary Health Care Corporation in Doha, Qatar over the period March 2013 to August 2014. Socio-demographic, behavioral and clinical data were collected. Four hundred and six cervical smears and 292 blood samples were included in the study. HPV typing was done using HPV type-specific primers-based real-time PCR, and Sanger sequencing. HPV-IgG and IgM were quantified using ELISA assays. The prevalence of HPV infection amongst Qatari and non-Qatari Arab women were 9.8% and 6.1%, respectively and 7.6% and 16.7% in women with normal and abnormal cytology, respectively. HPV 81 was the most commonly found genotype in women with normal cytology (34.5%), whereas HPV 81, 16 and 59 in women with abnormal cytology (25.0% each). All the HPV DNA positive women were seronegative and HPV-IgG prevalence was higher in Qatari women than in non-Qatari Arab women. None of the studied factors had any significant association with HPV-DNA positivity or HPV-IgG seropositivity. The overall identified HPV DNA prevalence and HPV seroprevalence among Arab women in Qatar were on the low side compared to global levels.

A decade of intestinal protozoan epidemiology among settled immigrants in Qatar.

BACKGROUND: The World Health Organization estimates that about 3.5 billion people worldwide are affected by intestinal parasitic infections. Reports have already emphasized the role of immigrants in outbreaks of parasitic diseases in industrialized countries. With the mass influx of immigrants to Qatar, patent intestinal parasitic infections have been observed. Herein, the prevalence of intestinal protozoan infections was analysed in 29,286 records of subjects referred for stool examination at the Hamad Medical Corporation over the course of a decade (2005 to 2014, inclusive). RESULTS: Overall prevalence of combined protozoan infections was 5.93 % but there were significant temporal trends, age and sex effects and those arising from the region of origin of the subjects. The most common protozoan was Blastocystis hominis (overall prevalence 3.45 %). Giardia duodenalis, Chilomastix mesnili, Entamoeba coli, Entamoeba hartmanni, Endolimax nana, Iodamoeba butschlii, Entamoeba histolytica/dispar, Cryptosporidium sp. and a single case of Isospora were also detected. The prevalence of combined protozoan infections, G. duodenalis and the non-pathogenic amoebae all declined significantly across the decade. That of B. hominis varied between years but showed no directional trend across years and there was no evidence that prevalence of E. histolyitica/dispar changed significantly. Protozoan infections were observed among all regional groups, but prevalence was higher among subjects from the Arabian Peninsula, Africa and Asia compared to those from the Eastern Mediterranean and Qatar. Prevalence was higher among male subjects in all cases, but age-prevalence profiles differed between the taxa. CONCLUSION: These results offer optimism that prevalence will continue to decline in the years ahead.

Helminth infections among long-term-residents and settled immigrants in Qatar in the decade from 2005 to 2014: temporal trends and varying prevalence among subjects from different regional origins.

BACKGROUND: Travel and migration from developing regions, where tropical diseases are common, to more developed industrialised nations can contribute to the introduction and subsequent spread of infections. With its rapidly expanding economy, Qatar has attracted vast numbers of immigrant workers in the last two decades, often from countries with poor socio-economic levels. Many used to arrive with patent intestinal parasitic infections. METHODS: We analysed the prevalence of helminth infections in a dataset of 29,286 records of subjects referred for stool examination at the Hamad Medical Corporation over the course of a decade (2005 to 2014, inclusive). RESULTS: Overall prevalence of combined helminth infections was low (1.86 %) but there were significant temporal trends, age and sex effects and those arising from the region of origin of the subjects. The most common helminths were hookworms (overall prevalence 1.22 %), which accounted for 70.1 % of cases, and therefore patterns for combined helminth infections were largely driven by hookworms. In both cases, and also in Trichuris trichiura and Ascaris lumbricoides, prevalence peaked in 2008, since when prevalence has been steadily falling. Helminth infections were largely concentrated among subjects from five Asian countries (Nepal, Bangladesh, Sri Lanka, India and Pakistan), and there was a highly biased prevalence in favour of male subjects in all cases. Prevalence of all three nematodes peaked in age class 7 (mean age 25.5 years, range = 20-29) and there were significant interactions between region of origin, sex of subjects and prevalence of hookworms. CONCLUSION: These results offer optimism that prevalence will continue to decline in the years ahead, especially if control is targeted at those most at risk of carrying infections.

The Qatar Biobank: background and methods.

BACKGROUND: The Qatar Biobank aims to collect extensive lifestyle, clinical, and biological information from up to 60,000 men and women Qatari nationals and long-term residents (individuals living in the country for ≥15 years) aged ≥18 years (approximately one-fifth of all Qatari citizens), to follow up these same individuals over the long term to record any subsequent disease, and hence to study the causes and progression of disease, and disease burden, in the Qatari population. METHODS: Between the 11(th)-December-2012 and 20(th)-February-2014, 1209 participants were recruited into the pilot study of the Qatar Biobank. At recruitment, extensive phenotype information was collected from each participant, including information/measurements of socio-demographic factors, prevalent health conditions, diet, lifestyle, anthropometry, body composition, bone health, cognitive function, grip strength, retinal imaging, total body dual energy X-ray absorptiometry, and measurements of cardiovascular and respiratory function. Blood, urine, and saliva were collected and stored for future research use. A panel of 66 clinical biomarkers was routinely measured on fresh blood samples in all participants. Rates of recruitment are to be progressively increased in the coming period and the recruitment base widened to achieve a cohort of consented individuals broadly representative of the eligible Qatari population. In addition, it is planned to add additional measures in sub-samples of the cohort, including Magnetic Resonance Imaging (MRI) of the brain, heart and abdomen. RESULTS: The mean time for collection of the extensive phenotypic information and biological samples from each participant at the baseline recruitment visit was 179 min. The 1209 pilot study participants (506 men and 703 women) were aged between 28-80 years (median 39 years); 899 (74.4%) were Qatari nationals and 310 (25.6%) were long-term residents. Approximately two-thirds of pilot participants were educated to graduate level or above. CONCLUSIONS: The pilot has proven that recruitment of volunteers into the Qatar Biobank project with intensive baseline measurements of behavioural, physical, and clinical characteristics is well accepted and logistically feasible. Qatar Biobank will provide a powerful resource to investigate the major determinants of ill-health and well-being in Qatar, providing valuable insights into the current and future public health burden that faces the country.

Reference ranges of lymphocyte subsets in healthy Qatari adults.

AIM: Determine reference ranges of lymphocyte subsets in healthy Qatari adults. PATIENTS & METHODS: Blood samples (n = 150) were investigated using four colors flow cytometery. RESULTS: The mean percentage and absolute values of the lymphocyte subsets were: CD3: 73.6 ± 6.1%; 2,072 ± 644 cells/µl; CD4: 41.1 ± 7.9%; 1,167 ± 396 cells/µl; CD8: 33.8 ± 7.1%; 967 ± 364 cells/µl; B cells (CD19(+)): 11.3 ± 3.9%; 318 ± 144 cells/µl and natural killer (NK) cells (CD16/56(+)): 16.5 ± 6.3%, 440 ± 401 cells/µl, respectively. The CD4/CD8 ratio was 1.3 ± 0.5. The ratio, CD3(+) and CD4(+) percentage and CD4(+) cell counts were significantly higher in females; CD8(+) and NK cell count and CD8(+) percentage were significantly higher in males. The impact of age was less certain. CONCLUSION: The reference values of lymphocyte subsets appear to be specific to this population, demonstrating the importance of establishing local reference ranges.

Molecular epidemiology and genotype distribution of Human Papillomavirus (HPV) among Arab women in the State of Qatar.

BACKGROUND: Human Papilloma Virus (HPV) infection is the major cause of cervical cancer worldwide. With limited data available on HPV prevalence in the Arab countries, this study aimed to identify the prevalence and genotypic distribution of HPV in the State of Qatar. METHODS: 3008 cervical samples, exclusively of women with Arabic origin residing in Qatar were collected from the Women's Hospital and Primary Health Care Corporation in Doha, State of Qatar. HPV DNA detection was done using GP5+/6+ primers based real time-polymerase chain reaction (RT-PCR) assay followed by the usage of HPV type specific primers based RT- PCR reactions and Sanger sequencing for genotype identification. RESULTS: Similar prevalence rates of HPV infection was identified in both Qatari and non-Qatari women at 6.2% and 5.9% respectively. HPV prevalence rate of 5.8% and 18.4% was identified in women with normal cytology and in women with abnormal cytology respectively. HPV 81, 11 and 16, in decreasing order were the most commonly identified genotypes. HPV 81 was the most frequent low-risk genotype among women with both normal (74.0%) and abnormal (33.3%) cytology. HPV 16 (4.6%) was identified as the predominant high-risk HPV genotype among women with normal cytology and HPV 16, HPV 18, and HPV 56 (22.2% each) were the most common identified high-risk genotypes in women with abnormal cytology. CONCLUSIONS: The overall HPV prevalence in Arab women in Qatar was identified as 6.1% with an increased HPV prevalence seen in women with abnormal cytology results and no significant trends seen with age. In contrast to Western countries, we report a varied genotypic profile of HPV with a high prevalence of low-risk HPV genotype 81 among the Arab women residing in Qatar.

Polymerase chain reaction ribotyping of Clostridium difficile isolates in Qatar: a hospital-based study.

BACKGROUND: Clostridium difficile infection (CDI) is not generally reported to public health authorities in the Middle East and its true prevalence remains largely unknown. The aims of this study were to determine the prevalence of CDI and its associated ribotypes among C. difficile isolates in Qatar. Influence of age and correlation with other risk factors e.g. proton pump inhibitor use, antibiotic use, existence of chronic conditions, etc was also investigated for CDI positive patients. METHODS: A total of 1,532 patients with suspected CDI were recruited from two hospitals between 2011 and 2012. C. difficile was identified using glutamate dehydrogenase (GDH) lateral flow assay and toxins A and B Enzyme Immunoassay (EIA). The C. difficile positive samples were then cultured for PCR-ribotyping. RESULTS: 122 of the 1,532 (7.9%) samples from individual patients were identified as C.difficile positive; and 79 of these were viably cultured (~65%). From these, 36 different PCR ribotypes were isolated, of which strains 258 (6 [7.6%]), 01/014/046 (5 [6.3%]), and 011/053/056/107 (4 [5%]) were the most prevalent. The prevalence of PCR-ribotype 027 was 1.3% (n = 1). An age of ≥65 years and treatment with proton pump inhibitors correlated with higher frequency of CDI. Treatment with third generation cephalosporins (50 [41%]) and piperacillin/tazobactam antibiotics (55 [45.1%]) was most frequently associated with CDI. CONCLUSION: The most common C. difficile ribotype identified in Qatar was 258, which is different from those found in North America, Europe and Asia. The prevalence of CDI was higher in Qatar than Europe; though comparable to other Middle Eastern countries. These findings underscore the importance of local surveillance to detect and control C. difficile infection.

Characterising the aetiology of severe acute gastroenteritis among patients visiting a hospital in Qatar using real-time polymerase chain reaction.

BACKGROUND: Acute gastroenteritis (AGE) remains a common cause of clinic visits and hospitalizations, though its aetiology has not been determined in Qatar. METHODS: We performed a prospective, emergency department-based study of 288 children and adults with AGE. Stool specimens were collected at presentation from June to November 2009. Faecal specimens were tested, using real-time PCR, for a panel of four viral (norovirus, adenovirus, astrovirus and rotavirus) and bacterial pathogens. RESULTS: Viral and bacterial pathogens were detected in 131 (45.5%) and 34 (12.2%) of the 288 patients recruited. The most commonly detected pathogens were norovirus (28.5%), rotavirus (10.4%), followed by adenovirus (6.25%) and astrovirus (0.30%). Norovirus was the most commonly detected viral pathogen amongst all the age groups with an almost even distribution in all age groups. Rotavirus and adenovirus were more common in children under 5 yr of age. Astrovirus was found in only one person. CONCLUSIONS: Viruses, especially noroviruses, are associated with severe diarrhoea in children and adults in Qatar. Further studies to confirm the findings and to explore the causes of illness among patients from whom a pathogen cannot be determined are needed.

Prevalence of Chlamydia trachomatis infection in the general population of women in Qatar.

OBJECTIVES: The Arabian Gulf region has limited epidemiological data related to sexually transmitted infections. The objective of this study was to estimate the prevalence of Chlamydia trachomatis infection among general population women in Doha, Qatar. METHODS: Endocervical swabs were collected from healthy women attending primary healthcare centres in Doha, June-December 2008. The specimens were tested for C trachomatis by a commercially available PCR-based assay. Data on basic socio-demographic characteristics, medical history and sexual behaviour were obtained using self-administered questionnaires. The prevalence of C trachomatis and of background variables were stratified by nationality, Qatari nationals versus non-Qatari residents. RESULTS: A total of 377 women were enrolled in the study, out of whom 351 (37.9% Qataris, 62.1% non-Qataris) were tested for the presence of C trachomatis in their specimens. The mean age of participants was 41.2 years, and the vast majority (93%, 95% CI 90.3 to 95.7) were married. The mean age at sexual debut was significantly lower among Qatari women compared with non-Qatari women (19.2 vs 22.2 years, respectively p<0.001), but the mean number of reported lifetime sexual partners (1.1 partner) was nearly the same in both groups (p=0.110). The prevalence of C trachomatis infection was 5.3% among Qatari women and 5.5% among non-Qatari women, with no statistically significant difference between both groups (p=0.923). CONCLUSIONS: The prevalence of C trachomatis among women was higher than expected, with no significant difference between Qatari nationals and expatriate residents. The higher prevalence may reflect, in part, the limited access to and use of chlamydia screening and management.