Confirmation of presumptive Legionella colonies on culture media according to ISO 11731:2017: Principles, problems and practice

AIMS

The ISO 11731 norm, published in 2017, describes a method to identify and enumerate Legionella based exclusively on the confirmation of presumptive colonies by subculturing them on BCYE and BCYE-cys agar (BCYE agar without L-cysteine).

METHODS AND RESULTS

Despite this recommendation, our laboratory has kept confirming all presumptive Legionella colonies by combining the subculture method with the latex agglutination and polymerase chain reaction (PCR) assays. Here, we show that the ISO 11731:2017 method adequately performs in our laboratory according ISO 13843:2017. We compared the performance of the ISO method in detecting Legionella in typical and atypical colonies (n = 7156) from health care facilities (HCFs) water samples to that of our combined protocol and we found a 2.1% false positive rate (FPR), underscoring the importance of combining agglutination test and PCR with subculture to achieve optimal confirmation. Lastly, we estimated the water system disinfection cost for HCFs (n = 7), that due to false positive results, would displayed Legionella values exceeding the threshold of risk acceptance established by the Italian guidelines.

CONCLUSIONS

Overall, this large-scale study indicates that the ISO 11731:2017 confirmation method is error-prone, leading to significant FPRs and higher costs for HCFs due to remedial actions on their water systems.

Antibody responses to BNT162b2 SARS-CoV-2 mRNA vaccine among healthcare workers and residents of long-term care facilities: A cohort study in Northern Italy

Background and Aims

Long-term care facilities (LTCFs) have been severely impacted by COVID-19, with a disproportionate amount of SARS-CoV-2 infections and related deaths occurring among residents.

Methods

This study is part of an ongoing multicenter, prospective cohort study conducted among healthcare workers (HCWs) and residents of 13 LTCFs in Northern Italy designed to evaluate SARS-CoV-2 specific immunoglobulin class G (IgG) titers before and following vaccination with Pfizer/BNT162b2 SARS-CoV-2 mRNA vaccine (two doses of vaccine, 21 days apart). Serum samples were obtained from participants (t0) before vaccination, and (t1) 2 weeks after and analyzed to determine anti-S1 IgG antibodies.

Results

Five hundred and thirty-four participants were enrolled (404 subjects participated in both blood draws). Seropositivity was 50.19% at t0 and 99% at t1, with a significant difference in IgG titers. A higher proportion of residents were seropositive at t0 compared with HCWs, with significantly higher IgG titers among residents at both t0 and t1. Pre-existing immunity also had a significant effect on postvaccination IgG titers. However, a significant difference in titers at t1 between HCWs and residents considering only participants seropositive at t0 was found, with higher median titers among previously seropositive residents.

Conclusion

Findings of this study provide scientific evidence endorsing the policy of universal vaccination in LTCFs.

Seroprevalence of infection-induced SARS-CoV-2 antibodies among healthcare users of Northern Italy - results from two serosurveys (October-November 2019 - September-October 2021)

Objectives

The objective was to estimate the seroprevalence of SARS-CoV-2 in autumn 2019 (before case zero was identified in Italy) and 2021 among residual sera samples from health care users in the Piedmont region of northwestern Italy.

Methods

Two serosurveys were conducted. Using a semiquantitative method, samples were tested for the presence of immunoglobulin G (IgG) antibodies against the S1 domain of the spike protein. Samples with positive test results from the 2019 survey were independently retested using a multiplex panel to detect IgG antibodies against the receptor binding domain, S1 and S2 domains, and nucleocapsid. Samples with positive test results from the 2021 survey underwent repeat testing with enzyme-linked immunosorbent assay to detect anti-nucleocapsid IgG antibodies. Prevalence rates according to gender and age groups, together with their respective 95% confidence intervals (CIs), were calculated.

Results

Overall, the proportion of samples with positive test results was 2/353 in 2019 and 22/363 in 2021, with an estimated seroprevalence of 0.27% (95% CI 0-1.86) and 6.21% (95% CI 3.9-9.31) in 2019 and 2021 respectively.

Conclusion

Results of this study support the hypothesis that the virus was circulating in Italy as early as autumn 2019. The role of these early cases in broader transmission dynamics remains to be determined.

A New Culture Method for the Detection of Non-Tuberculous Mycobacteria in Water Samples from Heater-Cooler Units and Extracorporeal Membrane Oxygenation Machines

The isolation of non-tuberculous mycobacteria (NTM) from cultures is particularly laborious due to the potential overgrowth of coexisting non-acid fast bacilli. To reduce the overgrowth of these non-mycobacterial organisms, a decontamination step with NaOH or cetylpyridinium chloride is highly recommended before plating the samples on the culture medium. However, due to their toxicity, decontamination solutions tend to decrease NTM recovery from clinical and environmental samples. Here, we tested an alternative method for NTM recovery based on the use of NTM Elite agar, a selective medium that does not require a decontamination step. Using NTM Elite agar, we were able to detect non-tuberculous mycobacteria in 27.7% (30/108) of water samples analyzed. The average time to NTM detection was 18 days, but some strains required longer to grow, perhaps due to the stressful environmental conditions (periodical disinfection of devices). NTM Elite agar's effectiveness in inhibiting background flora was proven by the isolation of NTM from samples with and without background flora, showing no statistically significant differences in detection rates for different total viable counts of background flora (p = 0.4989). In conclusion, our findings indicate that effective NTM recovery from HCU- and ECMO-derived water samples can be achieved via filtration and direct culture of the filters on NTM Elite agar. This simple procedure can speed up laboratory work and provide an improved method, successfully resulting in low contamination and high detection rate, in addition to being less time-consuming. Its sensitivity and lack of a decontamination step make this protocol particularly useful for monitoring the effectiveness of device disinfection in hospital settings, even in the presence of low NTM loads. Reading timeframes should probably be extended to 7 weeks (i.e., well beyond the standard 4 weeks advised by the manufacturer), in order to isolate even the slow-growing mycobacteria. However, an extended incubation period is not necessary for exclusion of M. chimaera contamination of the devices, as M. chimaera isolation times do not generally exceed 3 weeks.

Cross-sectional study of SARS-CoV-2 seropositivity among health-care workers and residents of long-term facilities in Italy, January 2021

Long‐term care facilities (LTCFs) are high‐risk settings for SARS‐CoV‐2 infection. This study aimed to describe SARS‐CoV‐2 seropositivity among residents of LTCFs and health‐care workers (HCWs). Subjects were recruited in January 2021 among unvaccinated HCWs of LTCFs and hospitals and residents of LTCFs in Northern Italy. Information concerning previous SARS‐CoV‐2 infections and a sample of peripheral blood were collected. Anti‐S SARS‐CoV‐2 IgG antibodies were measured using the EUROIMMUN Anti‐SARS‐CoV‐2 QuantiVac ELISA kit (EUROIMMUN Medizinische Labordiagnostika AG). For subjects with previous COVID‐19 infection, gender, age, type of subject (HCW or resident), and time between last positive swab and blood draw were considered as possible determinants of two outcomes: the probability to obtain a positive serological result and antibody titer. Six hundred and fifty‐eight subjects were enrolled. 56.1% of all subjects and 65% of residents presented positive results (overall median antibody titer: 31.0 RU/ml). Multivariable models identified a statistically significant 4% decrease in the estimated antibody level for each 30‐day increase from the last positive swab. HCWs were associated with significant odds for seroreversion over time (OR: 0.926 for every 30 days, 95% CI: 0.860–0.998), contrary to residents (OR: 1.059, 95% CI: 0.919–1.22). Age and gender were not factors predicting seropositivity over time. Residents could have a higher probability of maintaining a seropositive status over time compared to HCWs.

Chemical susceptibility testing of non-tuberculous mycobacterium strains and other aquatic bacteria: Results of a study for the development of a more sensitive and simple method for the detection of NTM in environmental samples

The methods employed to detect non-tuberculous mycobacteria on environmental samples are essentially those classically used in clinical microbiology, which envisage a decontamination step to reduce the overgrowth of non-mycobacterial organisms before plating them on the culture medium. The aim of this study was to propose alternative culture techniques to improve non-tuberculous mycobacteria detection in environmental samples. We used artificially contaminated samples to compare the membrane filter washing procedure against direct plating of membrane filters on culture media in relation to M.chimaera and M.chelonae recovery efficiency. Moreover, we compared the efficacy of NTM Elite agar in inhibiting the growth of aquatic bacteria with that of cetylpyridinium chloride and N-acetyl-L-cysteine sodium hydroxide decontamination treatments. The washing procedure yielded a low release of both mycobacterium strains (6.6% for Mycobacterium chimaera and 7.5% for Mycobacterium chelonae) from the membrane filters; on the contrary, direct plating of membrane filters led to a 100% cell recovery. Water sample pretreatment with N-acetyl-L-cysteine sodium hydroxide (1%), despite achieving complete suppression of non-acid fast bacilli, caused a reduction in mycobacteria growth. Decontamination with cetylpyridinium chloride (0.005%) was found to be ineffective against Methylobacterium spp. and Burkholderia multivorans. NTM Elite agar was ineffective against B. multivorans, but it inhibited the growth of all other aquatic bacteria. Our results indicate that NTM Elite agar provides a valid alternative method of recovering non-tuberculous mycobacteria from environmental samples. It does not involve a decontamination step and provides greater recovery efficiency by skipping the washing step and directly plating the filters on the media.

The use of BCYE medium for the detection of Legionella in environmental water samples: an appropriate update to ISO 11731:2017 standard?

We evaluated the diagnostic performances of 2 media (BCYE, MWY) on 951 Legionella-positive hospital water samples. MWY allowed detecting Legionella in 89.2% of samples, but in 10.8% (103/951) Legionella was found on BCYE plates only. In samples where Legionella was isolated with other microorganisms (663/951), MWY was essential to detect the majority of positive samples (349/663, 52.6%), as fewer plates resulted unreadable; however, in those containing Legionella only, a higher frequency of positive samples was recorded with BCYE (94.8%, 273/288) compared to MWY (85.1%, 245/288). Considering the 484 concordant positive samples, overall Legionella counts were significantly higher on BCYE (P = 0.0029), with 47% of samples showing higher counts on BCYE compared to MWY plates. Furthermore, discordant samples (positive on only one medium) showed different relative proportions between Legionella pneumophila and non-pneumophila, the latter being found more frequently on BCYE only (P = 0.0296).Our findings confirm the appropriateness of the ISO 11731:2017 update.

First assessment of covid-19 vaccine response in a population at risk

Introduction

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has led to a global pandemic. Currently, the diagnosis of COVID-19 is confirmed by detecting SARS-CoV-2 via RealTime-RT-PCR in rhino-pharyngeal swab. Serological test is required to evaluate a previous exposure to the virus, as well as antibody response. The aim of this multicentric study is to analyse the antibody response following COVID-19 vaccination in healthcare workers and guests of nursing homes, and to determine differences between subjects with or without a confirmed previous infection.

Methods

Our study included 657 subjects, recruited from guests and healthcare workers of nursing homes in the Piedmont region. 10 days after the completion of the vaccination cycle, a blood sample was taken from the subjects to measure IgG against SARS-CoV-2 spike protein. Serological testing was performed using an enzyme immunoassay kit (EUROIMMUN Anti-SARS-CoV-2 QuantiVac ELISA). We performed statistical analysis with R software.

Results

We recruited 657 subjects aged between 19 to 106. Among them, 404 had a previous infection and 253 didn't have a known previous infection. The serological examination resulted positive in 655 subjects and negative in 2 (X¯ IgG 1095 RU/ml). Samples with titer> 1200 RU/ml will be further diluted to identify the titer and differences from the baseline situation.

Conclusions

This study analyses neutralizing antibodies, which should prevent the virus from binding to target cells via spike protein. According to literature, immunological response to vaccine presents a great variability of antibodies level in the study population. However, no significantly correlations were found between the available variables. Preliminary data show the presence of a very intense antibody response after active vaccine immunization both in subjects with previous infection and in the rest of the study population.

Key messages

Covid-19 vaccine response in a population at risk. Differences between subjects with or without a confirmed previous infection.

Preliminary assessment of COVID-19 serological situation in a high-risk cohort

Introduction

Studies on the duration of immune response in subjects with COVID-19 could facilitate understanding of how immunity develops and persists during the natural course of infection, as well as providing epidemiological information useful in public health decisions on the use of vaccines. The study aims to analyse antibody response in a cohort of subjects with high-risk of exposure to SARS-CoV-2 due to the long-term care facility environment.

Methods

We recruited 657 subjects between guests and healthcare workers from Piedmontese nursing homes. IgG directed against the S1 domain of SARS-CoV-2 spike protein were assayed on serum. We used EUROIMMUN kit, which exploits ELISA method. Reference values are (RU/mL): positive ≥ 11; borderline 8 ≤ value < 11; negative < 8.

Results

Among the 657 subjects, we examined 494 health workers and 163 guests. The average age was 56.2. In relation to COVID-19, 402 subjects had a previous infection, 255 had not. About serology: positive 369; negative 261; borderline 27. The mean of the IgG values was 35.68 RU/mL. Swabs/serology: 77.36% with previous infection were positive to serology, 18.66% negative; of all subjects who were always negative to swabs, 72.94% were negative, 22.74% positive. Moreover, the mean time elapsed from positive swab to serology test was 144.08 days.

Conclusions

Preliminary results show that the antibody response is present and persistent in the study population, even a long time after the infection. According to literature, antibody persistence has great variability in our population, as no statistically significant correlations were found between antibody titer and other variables such as time elapsed since infection. The examined sample, belonging to high-risk category (long-term care facilities), is most likely to present repeated exposure to SARS-CoV-2, highlighted by the seropositivity of never infected subjects. These findings might help policy makers better address resources regarding vaccines.

Key messages

Antibody response is present and persistent in the study population, even a long time after the infection. Antibody persistence has great variability in our population, as no statistically significant correlations were found between antibody titer and other variables such as time elapsed since infection.

Comparison of BCYEα+AB agar and MWY agar for detection and enumeration of Legionella spp. in hospital water samples

Background

This study illustrates for the first time the performance (sensitivity and selectivity) of the selective medium BCYEα +AB suggested by the new edition of ISO 11731 for legionella isolation and enumeration. We compared the efficacy of the selective BCYEα +AB medium with that of the highly selective MWY medium.

Results

Legionella spp. was detected in 48.2 and 47.1% of the samples by BCYEα +AB and MWY agar, respectively. For optimal detection of Legionella spp., most protocols recommend using selective media to reduce the number of non-Legionella bacteria. Agreement between the two media was 86.7%.

Conclusions

According to the results, both media have a very similar performance and they both have advantages and disadvantages over each other. In AB medium there is the risk of being less selective so more interfering microbiota may grow but in MWY medium there is the risk of being too selective. The low selectivity of the AB medium could be resolved if other treatments are applied after filtration, e.g. acid and/or heat treatment, but it must be taken into account that these treatments still reduce the number of viable Legionella. In conclusion, we recommend using MWY as a selective medium for the detection of Legionella spp. as it is easier discern suspected colonies and facilitate the final Legionella spp. count.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02109-1.

Real-time PCR, the best approaches for rapid testing for Mycobacterium chimaera detection in heater cooler units and extracorporeal membrane oxygenation

According to recent investigations, the risk of M. chimaera contamination of heater-cooler units (HCUs) has reached global proportions. Our aim was to field evaluate a protocol for early detection of M. chimaera contamination. We assessed the presence of viable M. chimaera in 395 water samples obtained from 48 devices (HCUs and extracorporeal membrane oxygenation) by Real Time PCR. Thirty devices were NTM positive, of which 14 were contaminated with M. chimaera. The most frequently contaminated devices were the Stockert 3T. Noteworthy, Stockert 3T devices were positive for M. chimaera. In conclusion, this study introduces novel PMA-PCR designed to specifically detect M. chimaera in HCUs and ECMO devices; this method can replace the culture method for continuous microbiological surveillance. The timely detection of M. chimaera contamination can then be used to improve effective management of the devices.

Failure to eradicate non-tuberculous mycobacteria upon disinfection of heater-cooler units: results of a microbiological investigation in northwestern Italy

BACKGROUND

Heater-cooler units (HCUs) used during cardiopulmonary bypass may become colonized with non-tuberculous mycobacteria (NTM), including Mycobacterium chimaera. Recently, a worldwide investigation conducted in hospitalized infected patients has detected M. chimaera in several Stockert 3T HCUs manufactured by LivaNova.

AIM

Microbiological surveillance on Stockert 3T (LivaNova) and Maquet HCU40 (Getinge) devices as well as an evaluation of the efficacy of their recommended decontamination protocols.

METHODS

A total of 308 water samples were collected from 29 HCUs: 264 samples were collected from 17 Stockert 3T HCUs and 44 samples from 12 Maquet HCU40 devices. Samples were tested for total viable counts (TVCs) at both 22 and 36°C, Pseudomonas aeruginosa, coliform bacteria, and NTM. The microbiological surveillance began in June 2017 and ran until October 2019.

FINDINGS

A total of 308 HCU water samples were analysed, 65.5% of which yielded NTM. The most frequently colonized device with NTM was the Stockert 3T (88.2%), with a frequency of positive samples of 59.5% (157/264). The Maquet HCU40 devices less frequently yielded NTM (33.3%), with a frequency of positive water samples of 13.6% (6/44). Disinfection procedures were effective in reducing TVCs of bacteria with the exception of NTM species. NTM were detected in both pre-disinfection (50.1%) and post-disinfection (55.7%) samples, and no significant association was found between disinfection and NTM results both in Stockert 3T and Maquet HCU40 devices.

CONCLUSION

This study suggests that manufacturers' procedures for disinfection are ineffective and/or inadequate. Until effective disinfection protocols become available, the only way to minimize the risk of NTM contamination is to closely monitor the water quality in the HCU, keep it as clean as possible, and treat it like any other biohazardous material.

Sensitivity and Selectivity of Two Commercially Available Media for Legionella spp. Recovery from Environmental Water Samples

The quality control of culture media used for Legionella spp. isolation and enumeration is paramount to achieve a satisfactory degree of comparability among water testing results from different laboratories. Here, we report on a comparative assessment of the sensitivity and selectivity of MWY and BCYEα media supplied by two different manufacturers (i.e., Xebios Diagnostics GmbH and Oxoid Ltd) for the detection of Legionella spp. from environmental water samples. Even though our analysis showed an excellent agreement between the recovery rates of the four media tested (90.5%), the quantitative recovery of Legionella spp. colonies using Xebios media was significantly greater than that achieved by Oxoid media (P = 0.0054). Furthermore, the sensitivity of detection was significantly higher when samples were plated on MWY ^Xebios agar (P = 0.0442), while the selectivity of MWY appeared to be the same regardless of the manufacturer. Furthermore, MWY^Xebios agar favored the growth of much larger colonies compared to those observed on MWY^Oxoid agar. Finally, MWY^Xebios medium enhanced the recovery of non-pneumophila Legionella species. Collectively, our findings demonstrate that quality control is crucial to ensure high selectivity and sensitivity of the culture media used for the detection and enumeration of Legionella spp. from environmental water resources. As water remediation measures strictly depend on Legionella spp. recovery, culture protocol standardization, as well as quality control of the culture media, is essential to achieve intra- and interlaboratory reproducibility and accuracy.

Reduction of turnaround time for non-tuberculous mycobacteria detection in heater-cooler units by propidium monoazide-real-time polymerase chain reaction

BACKGROUND

Invasive non-tuberculous mycobacteria (NTM) infections are emerging worldwide in patients undergoing open-chest cardiac bypass surgery exposed to contaminated heater-cooler units (HCUs). Although this outbreak has been investigated by culturing bacteria isolated from HCU aerosol and water samples, these conventional methods have low-analytic sensitivity, high rates of sample contamination, and long turnaround time.

AIM

To develop a simple and effective method to detect NTM in HCUs by real-time polymerase chain reaction (PCR), with a short laboratory turnaround time and reliable culture results.

METHODS

A total of 281 water samples collected from various HCUs at seven Italian hospitals were simultaneously screened for NTM by a propidium monoazide (PMA)-PCR assay and by conventional culture testing. The results were analysed with culture testing as the reference method.

FINDINGS

(i) The agreement between culture testing and PMA-PCR was 85.0% with a cycle threshold (C_T) cut-off value of <38 vs 80.0% with a C_T of <43, with a moderate Cohen's κ-coefficient; (ii) the C_T cut-off value of <42 was deemed more suitable for predicting positive specimens; (iii) given the low concentration of target DNA in water samples, the minimum volume to be tested was 1 L.

CONCLUSION

The use of PMA-PCR for fast detection of NTM from environmental samples is highly recommended in order to ascertain whether HCUs may represent a potential source of human exposure to NTM. This reliable and simple method reduces laboratory turnaround time compared to conventional methods (one to two days vs eight weeks, respectively), thereby improving control strategies and effective management of HCUs.

Reduction of turnaround time for non-tuberculous mycobacteria detection in heater-cooler units by propidium monoazide-real-time polymerase chain reaction

BACKGROUND

Invasive non-tuberculous mycobacteria (NTM) infections are emerging worldwide in patients undergoing open-chest cardiac bypass surgery exposed to contaminated heater-cooler units (HCUs). Although this outbreak has been investigated by culturing bacteria isolated from HCU aerosol and water samples, these conventional methods have low-analytic sensitivity, high rates of sample contamination, and long turnaround time.

AIM

To develop a simple and effective method to detect NTM in HCUs by real-time polymerase chain reaction (PCR), with a short laboratory turnaround time and reliable culture results.

METHODS

A total of 281 water samples collected from various HCUs at seven Italian hospitals were simultaneously screened for NTM by a propidium monoazide (PMA)-PCR assay and by conventional culture testing. The results were analysed with culture testing as the reference method.

FINDINGS

(i) The agreement between culture testing and PMA-PCR was 85.0% with a cycle threshold (C_T) cut-off value of <38 vs 80.0% with a C_T of <43, with a moderate Cohen's κ-coefficient; (ii) the C_T cut-off value of <42 was deemed more suitable for predicting positive specimens; (iii) given the low concentration of target DNA in water samples, the minimum volume to be tested was 1 L.

CONCLUSION

The use of PMA-PCR for fast detection of NTM from environmental samples is highly recommended in order to ascertain whether HCUs may represent a potential source of human exposure to NTM. This reliable and simple method reduces laboratory turnaround time compared to conventional methods (one to two days vs eight weeks, respectively), thereby improving control strategies and effective management of HCUs.

Colonization by Pseudomonas aeruginosa of dental unit waterlines and its relationship with other bacteria: suggestions for microbiological monitoring

Pseudomonas aeruginosa is an environmental bacterium, ubiquitous in aquatic habitats and water distribution systems, including dental unit waterlines (DUWLs). We investigated the prevalence of P. aeruginosa in DUWLs from private dental settings. We also analyzed the relationship between P. aeruginosa contamination and the presence of Legionella spp. and total viable count (TVC) in order to suggest a simple and inexpensive protocol to test the quality of water from DUWLs. We detected and quantified P. aeruginosa both by culture and by a PMA (propidium monoazide)-qPCR method. Overall, we detected P. aeruginosa in 17 samples using the PMA-qPCR and in 11 samples using the culture. All culture-positive samples were positive with the PMA-qPCR too, with an agreement between the two methods of 93% and a Cohen's kappa coefficient of κ = 0.747 (good concordance). Comparing results with results of our previous study, we noted that (a) P. aeruginosa was isolated only from DUWLs with high TVC and (b) five out of six Legionella-positive samples were negative for Pseudomonas spp. Our final suggestion is that the cleanliness of DUWLs should be assessed by TVC because it is a good indicator of the presence of pathogens such as Legionella spp. and P. aeruginosa.

Characterisation and improvement of a reference cylindrical sonoreactor

This paper describes theoretical and experimental methods for characterising the performance of a 25 kHz sonochemical reactor (RV-25), which is being developed as a reference facility for studying acoustic cavitation at the National Physical Laboratory (NPL). Field measurements, acquired in different locations inside the sonoreactor, are compared with finite element models at different temperatures, showing that relatively small temperature variations can result in significant changes in the acoustic pressure distribution (and consequent cavitation activity). To improve stability, a deeper insight into the way energy is transferred from the power supply to the acoustic field is presented, leading to criteria - based on modal analysis - to dimension and verify an effective temperature control loop. The simultaneous use of measurements and modelling in this work produced guidelines for the design of multi-frequency cylindrical sonoreactors, also described.

Design of a laboratory for experiments with a pulsed neutron source

We present the results of a neutron shielding design and optimisation study performed to reduce the exposure to radiological doses arising from a 14 MeV pulsed neutron generator (PNG) having a maximum emission strength of 2.0 x 10(8) neutrons s(-1). The source was intended to be used in a new irradiation facility for the realisation of an experiment on acoustical cavitation in liquids. This paper describes in detail how the facility was designed to reduce both neutron and gamma-ray dose rates to acceptable levels, taking into account the ALARP principle in following the steps of optimisation. In particular, this work compares two different methods of optimisation to assess neutron dose rates: the use of analytical methods and the use of Monte Carlo simulations (MCNPX 2.4). The activation of the surrounding materials during operation was estimated using the neutron spectra as input to the FISPACT 3.0 code. The limitations of a first-order analytical model to determine the neutron activation levels are highlighted. The impact that activation has on the choice of the materials to be used inside the laboratory and on the waiting time before anyone can safely enter the room after the neutron source is switched off is also discussed.