Biomedical subjects

Thor Axel Stenström

Publications and source records attributed to Thor Axel Stenström.

7 recordsLinked to original sources

PubMed2006

Short- and long-term variations of norovirus concentrations in the Meuse river during a 2-year study period.

Faecally impacted surface waters used for drinking water production may encompass risk for norovirus infections. To be able to assess a possible health risk, noroviruses should be quantified and fluctuations identified. In 2001, norovirus concentrations in the river Meuse displayed a seasonal distribution with high peaks during wintertime as determined by RT-PCR on serially diluted RNA. An intensified day-by-day sampling scheme in the winter of 2002/2003 revealed that the winter peak consisted of several peaks of varying duration and magnitude, possibly due to contamination events in the catchment. The highest estimated concentration was 1700 PCR-detectable units per litre (95% CI 250-8000), which if coinciding with failing treatment could lead to significant numbers in drinking water. Adaptive dynamic filtering was shown to adequately predict subsequent sample concentrations. If valid, such analyses could prove to be useful as early warning systems in risk management of water sources.

Netherlands↗

PubMed2006

Drinking water consumption patterns in Sweden.

Estimates on drinking water consumption are necessary in risk assessments on microbial hazards in drinking water. Large differences in consumption habits between countries have been reported. In order to establish estimates for the Swedish population, water consumption data from a waterborne outbreak investigation (157 people), a small water consumption study (75 people) and a large study on health and environmental factors (10,957 people) were analysed. A lognormal distribution for the daily direct/cold water intake in litres with mu = - 0.299 and sigma = 0.570 was fitted to the quantitative data, representing the general population. The average daily consumption of tap water as plain drinking water and as heated tap water, e.g. in coffee and tea, was 0.86 +/- 0.48 l and 0.94 +/- 0.69 l, respectively. Women consumed more cold tap water than did men, while men appeared to have a higher consumption of heated tap water. Cold tap water intake was highest in the oldest age group, (> or =70 years). The consumption of bottled water was very low (mean 0.06 l/d) when compared to other countries.

Adult↗

PubMed2004

Artificial groundwater treatment: biofilm activity and organic carbon removal performance.

The artificial recharge of sand aquifers with raw source waters is a means both explored and utilised by many water utilities to meet the future potable water demands for increasing urban populations. The microbial ecology within these systems is however, poorly understood, as is the role that microbial biofilms play in the quality of finished water. Knowledge of the ability of biofilm bacteria to metabolise natural organic matter (NOM) is limited, particularly in respect to the degradation of normally recalcitrant hydrophilic and hydrophobic humic acid fractions by sessile and planktonic microbial consortia within sand aquifer systems. To simulate the artificial recharge of sand aquifers that were proposed for the Greater Stockholm Area, four separate 4 m deep sand columns were fed raw lake water and examined over a 45-week study period. The simulated aquifer system (hydraulic retention time 9-16 h) demonstrated the removal of total organic carbon (TOC) (10+/-5%), direct total counts (DTC) of bacteria (74+/-11%), heterotrophic plate count (HPC) bacteria (87+/-5%) and assimilable organic carbon (AOC) (87+/-5%), thereby fulfilling an important barrier function, except for the removal of TOC. Hydrophilic humic acid fractions were more readily metabolised by microbiota (HPC and EUB338-positive cells) harvested from the raw source water (SSM-W), whilst hydrophobic humic acid fractions promoted higher activity by microbiota harvested from the sand matrix (SSM-S). The apparent low activity demonstrated by biofilm microbiota (approximately 40% and 25% of DTC were positive to EUB338 probing for sand matrix and slide biofilms, respectively) could be attributed to the highly recalcitrant nature of the organic loads, whilst at the same time explain the poor removal of TOC. Following nutrient activation (by the PAC assay) nonetheless, a 3-fold increase in the percentage of EUB-positive bacteria was observed on glass slides. Furthermore, the incubation of SSM-S with R2A increased probe-active cells from 57+/-8% to 75+/-7% of DTC and at the same time increased SSM-W from 38+/-8% to 50+/-10%. Whilst these results may imply a good potential for the biological treatment of water by shallow sand aquifers, further work should address the poor removal of TOC observed in this study.

Biodegradation, Environmental↗

PubMed2004

Pivmecillinam and adverse birth and neonatal outcomes: a population-based cohort study.

A previous study unexpectedly showed an increased, statistically imprecise, risk of low Apgar score in children of women redeeming prescriptions for pivmecillinam in late pregnancy. To improve statistical precision we extended the previous dataset with data for 5 more y, and in addition added more neonatal outcomes. We thus examined the risk of adverse birth and neonatal outcomes among pregnant users of pivmecillinam based on population-based registries in North Jutland County, Denmark. We included 63,659 women with a live birth, or stillbirth after the 28th week of gestation. 2031 had redeemed prescriptions for pivmecillinam any time during pregnancy, 559 in the first trimester and 371 within 28 d before delivery. Adjusted odds ratios were: birth defects 0.83 (95% confidence interval (95% CI) 0.53-1.32) for exposure during first trimester, preterm delivery 0.96 (95% CI 0.79-1.18) and low birth weight 0.79 (95% CI 0.52-1.20) for exposure any time during pregnancy, and stillbirth 1.19 (95% CI 0.30-4.80), low Apgar score 1.17 (95% CI 0.37-3.66), hypoglycaemia 1.03 (95% CI 0.53-2.00), and respiratory distress syndrome 0.79 (95% CI 0.38-1.68) for exposure within 28 d before delivery. Use of pivmecillinam during pregnancy did not appear to increase the risk of adverse birth and neonatal outcomes; however, statistical precision is still low.

Abnormalities, Drug-Induced↗

PubMed2003

Faecal contamination of greywater and associated microbial risks.

The faecal contamination of greywater in a local treatment system at Vibyåsen, north of Stockholm, Sweden was quantified using faecal indicator bacteria and chemical biomarkers. Bacterial indicator densities overestimated the faecal load by 100-1000-fold when compared to chemical biomarkers. Based on measured levels of coprostanol, the faecal load was estimated to be 0.04 g person(-1) day(-1). Prevalence of pathogens in the population and the faecal load were used to form the basis of a screening-level quantitative microbial risk assessment (QMRA) that was undertaken for rotavirus, Salmonella typhimurium, Campylobacter jejuni, Giardia lamblia and Cryptosporidium parvum. The different exposure scenarios simulated--direct contact, irrigation of sport fields and groundwater recharge--gave unacceptably high rotavirus risks (0.04 < Pinf < 0.60) despite a low faecal load. The poor reduction of somatic coliphages, which were used as a virus model, in the treatment was one main reason and additional treatment of the greywater is suggested. Somatic coliphages can under extreme circumstances replicate in the wastewater treatment system and thereby underestimate the virus reduction. An alternative QMRA method based on faecal enterococci densities estimated similar risks as for rotavirus. Growth conditions for Salmonella in greywater sediments were also investigated and risk modelling based on replication in the system increased the probability of infection from Salmonella 1000-fold, but it was still lower than the risk of a rotavirus infection.

Bacteria↗

PubMed2002

Faecal contamination of source-separated human urine based on the content of faecal sterols.

Transmissible pathogens in source-separated human urine, intended for reuse in agriculture, mainly originate from faeces that cross-contaminate the urine. The health risks associated with the enteric pathogens will largely be dependent on their initial concentration and their inactivation during storage in the urine. Faecal sterols have proven stable in urine and can, rather than indicator bacteria, be used to quantify the faecal cross-contamination. In this study, urine collection tanks were sampled and ratios between various faecal sterols were used to determine if the urine was contaminated by faeces. Twenty-two percent of samples from the upper part of the tanks and 37% of samples from the bottom sludge were found to be contaminated. Coprostanol concentrations in the contaminated urine samples corresponded to a mean faecal contamination of 9.1+/-5.6 mg l(-1) urine. E. coli was absent in a majority of the samples. Faecal streptococci and clostridia were enumerated but not found to correlate with coprostanol concentrations in contaminated samples.

Agriculture↗

PubMed2002

Microbial risk assessment of source-separated urine used in agriculture.

A screening-level quantitative microbial risk assessment (QMRA) was undertaken for a urine separating sewerage system. Exposures evaluated included the handling of stored and unstored urine as well as consumption of crops fertilised with urine. Faecal cross-contamination was the source of risk and Campylobacter jejuni, Cryptosporidium parvum and rotavirus were the organisms chosen to represent different groups of enteric pathogens. Accidental ingestion of unstored urine implied a high risk (Pinf = 0.56) for infection from rotavirus whereas the risks for infection from bacteria and protozoa were approximately 1:10 000. After six months storage at 20 degrees C the risk for viral infections by accidental ingestion of 1 ml of urine was < 10(-3), the suggested acceptable risk benchmark. Ingestion of crops contaminated with urine resulted in risks of < 10(-5) after a 3-week (<10(-7) after 4 weeks) withholding period between fertilising and harvesting.

Agriculture↗