Table 1.
Characteristics of CDC’s National Wastewater Surveillance System (NWSS) sampling sites and samples, September 1, 2020 – December 31, 2022a.
| September–December 2020 | January–December 2021 | January–December 2022 | December 2022b | |
|---|---|---|---|---|
| Characteristics of wastewater sampling sites | ||||
| Sites, no. | 295 | 671 | 1750 | 1567 |
| Sites actively collecting samples at year’s end, no.c | 293 | 621 | 1567 | 1567 |
| Millions of persons served by all sites, no. (% of U.S. population)d | 38 (12) | 65 (20) | 150 (45) | 145 (44) |
| Thousands of persons served per site, median (IQR) | 24 (10, 84) | 21 (8, 75) | 20 (6, 66) | 22 (7, 73) |
| Site location, no. (%) | ||||
| WWTP | 287 (97) | 617 (92) | 1546 (88) | 1398 (89) |
| Upstream of a WWTP | 8 (3) | 54 (8) | 204 (12) | 169 (11) |
| Targets included in testing, no. (%)e | ||||
| SARS-CoV-2 only | 295 (100) | 671 (100) | 1289 (74) | 1107 (71) |
| SARS-CoV-2 and MPXV | 0 (0) | 0 (0) | 461 (26) | 460 (29) |
| WWTP size in million gallons of wastewater received per day, median (IQR) | 8 (3,21) | 7 (3,20) | 6 (2, 17) | 6 (2, 18) |
| Site management, no. (%) | ||||
| Local Health Department | 0 (0) | 46 (7) | 58 (3) | 49 (3) |
| State Health Department | 295 (100) | 625 (93) | 1201 (69) | 1072 (68) |
| Commercial Contractor | 0 (0) | 0 (0) | 394 (23) | 349 (22) |
| Academic Partner Program | 0 (0) | 0 (0) | 97 (6) | 97 (6) |
| Sites located on tribal lands, no. (%) | 0 (0) | 0 (0) | 11 (1) | 7 (0)f |
| Average percentage of wastewater from industrial sources received by WWTP, median (IQR)g | 5 (2,12) | 5 (2,13) | 5 (1,10) | 5 (2, 12) |
| WWTPs receiving wastewater from a combined sewer system, no. (%)g,h,i | 34 (26) | 70 (34) | 159 (44) | 149 (44) |
| Laboratories testing samples, no. | 23 | 58 | 104 | 78 |
| No. of samples collected per site per week, median (IQR) | 1 (1,2) | 1 (1, 2) | 2 (1, 2) | 2 (1, 2) |
| Characteristics of wastewater samples | ||||
| Samples collected, no. | 6062 | 36,030 | 111,511 | 10,965 |
| Time (in days) between sample collection and testing, median (IQR) | 2 (1, 4) | 2 (1, 4) | 2 (1, 4) | 2 (1, 4) |
| Sewage travel time (in hours) from sewage source to sampling site, median (IQR) | 9 (5, 15) | 9 (5, 15) | 6 (3,12) | 6 (3, 12) |
| Sample collection method, no. (%)h,j | ||||
| Grab | 438 (7) | 4460 (12) | 12,912 (12) | 1308 (12) |
| Manual composite | 0 (0) | 624 (2) | 3210 (3) | 296 (3) |
| Flow-weighted composite | 3613 (60) | 18,826 (52) | 44,665 (40) | 3968 (36) |
| Time-weighted composite | 2007 (33) | 12,120 (34) | 50,243 (45) | 5343 (49) |
| Passive | 0 (0) | 0 (0) | 481 (0) | 50 (0) |
| Sample typek | ||||
| Untreated wastewater | 5770 (95) | 31,933 (89) | 93,890 (84) | 8611 (79) |
| Wastewater post grit removal | 0 (0) | 1483 (4) | 12,981 (12) | 1819 (17) |
| Primary effluent | 0 (0) | 0 (0) | 90 (0) | 15 (0) |
| Primary sludge | 292 (5) | 2614 (7) | 4550 (4) | 520 (5) |
| Sample volume (in mL), median (IQR)l | 75 (40, 180) | 50 (40, 100) | 40 (40, 40) | 40 (20, 40) |
| Targets included in testing, no. (%)e | ||||
| SARS-CoV-2 only | 6062 (100) | 36,030 (100) | 104,865 (94) | 8406 (77) |
| SARS-CoV-2 and MPXV | 0 (0) | 0 (0) | 6646 (6) | 2559 (23) |
| PCR typeh,m | ||||
| RT quantitative PCR or quantitative PCR | 3524 (58) | 19,793 (55) | 50,236 (45) | 4655 (42) |
| RT digital PCR or digital PCR | 0 (0) | 592 (2) | 19,954 (18) | 1983 (18) |
| RT droplet digital PCR or droplet digital PCR | 2538 (42) | 15,645 (43) | 41,316 (37) | 4327 (39) |
| Endogenous wastewater control | ||||
| Pepper Mild Mottle Virus | 2866 (47) | 15,397 (43) | 65,315 (59) | 7263 (66) |
| CrAssphage | 877 (14) | 4065 (11) | 6448 (6) | 520 (5) |
| F+ RNA Coliphage | 0 (0) | 1 (0) | 192 (0) | 13 (0) |
| None | 2319 (38) | 16,567 (46) | 39,556 (35) | 3169 (29) |
Abbreviations: CDC, Centers for Disease Control and Prevention; NWSS, National Wastewater Surveillance System; no., number; IQR, Interquartile Range; WWTP, Wastewater Treatment Plant; MPXV, monkeypox virus; RT, Reverse Transcription; PCR, Polymerase Chain Reaction; mL, milliliters.
Sites were included if they collected ≥1 sample during the time period. Samples were included if they were collected during the time period.
Estimates for December 2022 are shown to summarize sites actively collecting samples at the end of the surveillance summary period.
Sites that collected samples in December of the respective year were considered to be actively collecting samples at year’s end.
U.S. Census Bureau population estimate as of April 1, 2020 (331,449,281 persons) were used to calculate percentages of the U.S. population served by NWSS sites. Sampling sites upstream in the wastewater collection network were excluded from population served estimates. Numbers are rounded to the thousand.
Targets included in testing were determined using data reported to NWSS as of December 31, 2022. No sites tested for MPXV only.
One tribal community is served by two sites.
Includes only WWTPs and not sites upstream of WWTPs.
Percentages were calculated excluding missing observations.
A combined sewer system is a sewer system that collects both sewage and stormwater.
Grab samples are from a single moment in time; composite samples are multiple grab samples pooled at a specified frequency over a set period of time; passive samples are collected from gauze or other absorbent material that is left in wastewater for a set period of time (typically several days). Composite samples can be manual (collected manually at different times), time-weighted (collected at preset time intervals using automated equipment), or flow-weighted (collected over regular time intervals with volume proportional to the flow rate using automated equipment).
Untreated wastewater is wastewater without any form of treatment applied to it. Post grit removal is wastewater after removal of large solids at a treatment plant but prior to a primary clarifier. Primary effluent is effluent from the primary clarifier. Primary sludge is sludge from the primary clarifier.
Calculations exclude sludge samples.
RT-PCR is used to quantify SARS-CoV-2 concentrations; PCR is used to quantify MPXV concentrations.