Risk-Based Critical Concentrations of Legionella pneumophila for

Where data for aerosol size from a given activity spanned multiple size bins (for example, for showers, aerosols were measured over ranges 1–2 μm, ...
0 downloads 0 Views 1MB Size
Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE

Ecotoxicology and Human Environmental Health

Risk-based critical levels of Legionella pneumophila for indoor water uses Kerry A. Hamilton, Mark T. Hamilton, William Johnson, Patrick Jjemba, Zia Bukhari, Mark LeChevallier, Charles N. Haas, and Patrick L. Gurian Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b03000 • Publication Date (Web): 10 Jan 2019 Downloaded from http://pubs.acs.org on January 11, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 40

1 2 3

Environmental Science & Technology

Risk-based critical concentrations of Legionella pneumophila for indoor residential water uses

4 5

Kerry A. Hamiltona,b*, Mark T. Hamiltonc, William Johnsond, Patrick Jjembad,

6

Zia Bukharid, Mark LeChevallierd, Charles N. Haase, P.L. Guriane

7 8

a

9

b The

School for Sustainable Engineering and the Built Environment, Arizona State University, Biodesign Institute Center for Environmental Health Engineering, Arizona State

10

University

11

c Microsoft

Machine Learning Research Group, 1 Memorial Drive, Cambridge, MA 02142

12

d American

Water Research Laboratory, 213 Carriage Lane, Delran, New Jersey 08075

13

e

Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104

14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

* Corresponding author. Kerry A. Hamilton. Mailing address: School for Sustainable Engineering ad the Built Environment, Arizona State University, 781 S Terrace Road, Tempe, Arizona 85281. E-mail address: [email protected]

30 1 ACS Paragon Plus Environment

Environmental Science & Technology

Page 2 of 40

31

ABSTRACT

32

Legionella spp. is a key contributor to the United States waterborne disease burden. Despite

33

potentially widespread exposure, human disease is relatively uncommon, except under

34

circumstances where pathogen concentrations are high, host immunity is low, or exposures

35

to small-diameter aerosols occurs. Water quality guidance values for Legionella are

36

available for building managers but are generally not based on technical criteria. To address

37

this gap, a quantitative microbial risk assessment (QMRA) was conducted using target risk

38

values in order to calculate corresponding critical concentrations on a per-fixture and

39

aggregate (multiple fixture exposure) basis. Showers were the driving indoor exposure risk

40

compared to sinks and toilets. Based on aggregate fixture exposures, critical concentrations

41

depended on the dose response model (infection vs. clinical severity infection, CSI), risk

42

target used (infection risk vs. disability adjusted life years on a per-exposure or annual

43

basis), and fixture type (conventional vs. water efficient or “green”). Median critical

44

concentrations based on exposure to a combination of toilet, faucet, and shower aerosols

45

ranged from ~10-2 to ~100 CFU per L and ~101 to ~103 CFU per L for infection and CSI dose

46

response models, respectively. As infection model results for critical L. pneumophila

47

concentrations were often below a feasible detection limit for culture-based assays, the use

48

of CSI model results for non-healthcare water systems with a 10-6 DALY pppy target (the

49

more conservative target) would result in an estimate of ~20 CFU per L (arithmetic mean of

50

samples across multiple fixtures and/or over time). Single sample critical concentrations with

51

a per-exposure-corrected DALY target at each fixture would be 1050 CFU per L (faucets),

52

4.3 × 105 CFU per L (toilets), and 25.2 CFU per L (showers). The absence of detectable L.

53

pneumophila may be appropriate for healthcare or susceptible population settings.

54 55 56

Keywords: Opportunistic pathogens; reverse quantitative microbial risk assessment

57

(QMRA); Legionella pneumophila; monitoring; building water quality; green building; efficient

58

water fixtures 2 ACS Paragon Plus Environment

Page 3 of 40

59

Environmental Science & Technology

1. Introduction

60

The importance of opportunistic pathogens such as Legionella has been increasing in

61

recent years, with Legionella spp. identified in recent US Centers for Disease Control and

62

Prevention (CDC) reports as the most common cause of waterborne disease outbreaks in

63

the US 1, 2. Legionella causes illness primarily in individuals with underlying health

64

conditions, and/or the elderly. Infection occurs when aerosols containing the bacteria are

65

inhaled or aspirated by a susceptible host. Recent reviews of environmental sources of

66

Legionella infections for sporadic and outbreak-associated cases 3-5 have emphasized the

67

importance of building water and cooling tower design and maintenance.

68

Monitoring routinely for Legionella is not typically practiced in premise plumbing systems

69

except when legionellosis cases are associated with a facility. While Legionella occurrence

70

in premise plumbing systems is not uncommon 6-13, monitoring for Legionella spp. on a

71

routine basis may not be a cost-effective measure 14. However, in order to validate aspects

72

of a water safety plan or management strategy, knowledge regarding interpretation of

73

Legionella spp. sampling results can provide information regarding potential risks.

74

Concentrations of L. pneumophila in cold tap water have been reported up to ~105 gene

75

copies per L 12, 15, 16 and ~104 colony forming units (CFU) per L 8, 10, 11, 17, and up to ~107 CFU

76

per L in hot water 8, 18 .

77

Existing water quality guidance values for Legionella spp. are available for building water

78

quality managers to inform the interpretation of measurements made in their water systems,

79

with potable water values ranging from 102 to 105 colony forming units (CFU) per L

80

associated with various desired water management actions (Table 1). In one case, a French

81

guideline specifies faucets > toilets.

391

It is noted here that previous assessments have demonstrated that the appropriate

392

measure of risk is the average of multiple exposures 56. Therefore when few data are

393

available in the literature to assess the time variability of L. pneumophila concentrations and

394

doses as in the current case, the annual exposure dose in this study can be regarded as a

395

time-averaged arithmetic dose even if time variability is significant 23, 45. Consequently, while

396

critical concentration values calculated in association with per-exposure scenarios might be

397

interpreted as a single sample concentration, critical concentration values associated with

398

annual risk scenarios might be interpreted as average concentrations over multiple sampling

399

events. A major limitation of the guidance documents summarized in Table 1 is that specific

400

sampling locations, frequency and timing of samples taken at a given location, and

401

statistically rigorous interpretation of sampling results is not specified. Simulating a full three-

402

dimensional space for concentration, exposure frequency, and risk is recommended as a

403

follow-on to this analysis and could help to customize risk findings to sampling results

404

observed at a particular building or other setting.

405

As demonstrated here (Figure 4), the ultimate decision regarding concentration limit

406

values is a function of which risk target is used (e.g., 10-4 annual probability of infection or

407

10-6 DALY pppy). Therefore, an analysis of how timing and extent of sampling might affect

408

critical concentration conclusions is beyond the scope of the current set of models but is

409

recommended for further analysis. As actions within the context of a water management plan

410

are typically developed on a case-by-case basis, the current modeling approach can allow

411

for lower-risk facilities to adopt different cut-offs for action.

412

For the combined exposures to multiple fixtures, the concentration values (median

413

10-2 to 103 L. pneumophila per L) overlap with some of the current guidance values (102 to

414

105 per L, with species not specified), although the guidance values would be on the higher

415

end of the simulated ranges. Specifically, median critical concentrations calculated in the

416

current models ranged from ~10-2 to ~100 CFU per L and ~101 to ~103 CFU per L for 15 ACS Paragon Plus Environment

Environmental Science & Technology

Page 16 of 40

417

infection and CSI dose response models, respectively. All guidance values reviewed were

418

above infection dose response model estimates, and the corresponding risk values for

419

various concentrations specified in the guidance can be interpreted directly from Figure 3.

420

Most guidance values were consistent with, or had some management actions associated

421

with, a CSI aggregate exposure model critical median concentration of