1

Appendix B.5: Comparison of NEEAR culturable water quality and health 

effects to EPA’s epidemiology studies from the 1980s : MEMO - NEEAR 

culture compared to 1980s data. 
2 

Cover Memo for Appendix B.5 Comparison of NEEAR culturable water quality and health 

effects to EPA’s epidemiology studies from the 1980s : MEMO - NEEAR culture compared 

to 1980s data. 

Purpose and Limitations of analysis in Appendix B.5 

The analysis described in Appendix B.5 was developed to evaluate whether the NEEAR culture 

data are consistent with the culture data used to develop the 1986 criteria. The raw data 

underlying the 1986 analyses have been lost over time. Only the summary statistics for the older 

data, as published in the 1986 criteria document and supporting documentation are available. 

Therefore EPA was not able to replicate the more modern statistical analyses that were used to 

evaluate the NEEAR data on the older dataset. 

The analyses in Appendix B.5 replicate the statistical methods used to evaluate the data that 

support the 1986 criteria and were conducted to provide historical perspective and evaluate 

whether the two datasets are consistent. These analyses consider the relative level of public 

health protection provided at the level of water quality specified in the new/revised RWQC. 

They do not define a new illness response for culture based FIB. The NEEAR illness response is 

best defined by the more sophisticated analyses published by Wade et al. 2008 and 2010. 

 
3

Comparison of NEEAR culturable water quality and health effects to EPA’s 

epidemiology studies from the 1980s : MEMO - NEEAR culture compared to 

1980s data

Executive Summary 

Objective

Compare observed culturable counts of enterococci and GI illness rates from the 1983/1984 epidemiology 

studies and NEEAR epidemiology studies. 

Summary

The NEEAR study data are generally consistent with data from 1983/1984 epidemiology studies. This 

analysis supports the continued use of the 1986 culture-based ambient water quality criteria for 

enterococci. However, there are specific conditions under which qPCR enterococci density may be a 

substantially better predictor of health effects than culturable enterococci.

Approach

Summarize culturable enterococci data from the NEEAR studies and compare the results to the 

1983/1984 studies. Identify similarities and differences between the NEEAR culturable enterococci and 

observed health effects data and the data from the 1983/1984 studies. 

Results

The POTW-impacted marine and freshwater NEEAR study data are qualitatively consistent with the data 

from the 1983/1984 epidemiology studies for culturable enterococci and observed excess GI illness. 

When the daily NEEAR data were aggregated by days of similar water quality, there were several 

conditions (beaches with low enterococci density and relatively high excess illness) that diverged from 

the previous study results. Subsequent investigation indicated that, in contrast to culturable enterococci, 

qPCR enterococci densities (for the aggregated data) generally increased with increasing rates of GI 

illness. This observation indicates that at certain sites and under specific conditions the qPCR enterococci 

density may correspond better to adverse health effect levels than culturable enterococci.

Limitations

These analyses are a limited evaluation of water quality data and are intended to compliment the reported 

epidemiological results. These analyses do not account for many of the covariate risk factors considered 

in EPA’s epidemiological analyses of NEEAR data such as age of participants, food consumption at the 

beach, or contact with sand. 

Background 

The epidemiological studies that underpin the 1986 Ambient Water Quality Criteria (AWQC) for 

recreational waters (Cabelli, 1983; Dufour, 1984) estimate illness levels for recreational water contact 
4

associated with specific levels of fecal indicator bacteria (U.S. EPA, 1986). The relationships between 

observed culturable counts of fecal indicator bacteria (FIB) and predicted illness levels in the 1986 

AWQC are based on observed seasonal geometric mean culturable FIB densities and average 

gastrointestinal (GI) illness rates from each study site. 

EPA’s recent NEEAR studies report statistically significant relationships between qPCR counts (CE 

and/or CCE) of enterococci and observed GI illness levels (note there was a change in the definition of GI 

illness from the earlier studies and the EPA Office of Research and Development has developed a 

translation factor for the different GI illness outcomes) (Wade et al., 2006; Wade et al., 2008; Wade et al., 

2010). The NEEAR studies were designed, in part to address many of the perceived or actual limitations 

in the earlier epidemiological studies. For example, new modern statistical and analytical techniques 

account for a wide range of covariates at a given level of water quality. Moreover, the NEEAR analyses 

are based on daily water quality and health observations rather than seasonal averages (as were used in 

the 1983/1984 epidemiological studies). The results from the NEEAR studies indicate that Enterococcus

qPCR levels are a stronger predictor of GI illness than culturable enterococci. However, swimmers 

exposed above the 1986 AWQC culturable values for enterococci did exhibit higher risks than nonswimmers or swimmers exposed below this value (Wade et al., 2008). 

Because culturable enterococci is likely to be included as one component of the 2012 new/revised 

recreational water quality criteria (RWQC), a relative comparison of the (culturable enterococci) results 

from the 1983/1984 and NEEAR epidemiology studies is important. However, as indicated above, the 

NEEAR studies employed different statistical methods compared to those reported in the 1980s, and a 

direct comparison of the results was not possible using the published results. Thus, this memorandum 

summarizes work to compile the NEEAR culturable enterococci data in a manner that is directly 

comparable to the 1983/1984 epidemiology studies and evaluate those comparisons. Tabular and 

graphical data summaries provide insights about the relative similarities and differences between the 

study results. 

Methods 

Water quality and health data from the NEEAR studies were provided by EPA ORD. Those data were 

consolidated into Excel spreadsheets. Tabular and graphical data summaries were then generated based 

on aggregation of the data by day, season, and days of similar culturable enterococci densities (water 

quality). The purpose of aggregating data by days of similar water quality was to balance the benefits and 

drawbacks of the daily and seasonal data. These aggregated data (by days of similar water quality) 

increase the robustness of water quality and health data over daily data while simultaneously increasing 

resolution over seasonal data. 

To facilitate a comparison between the NEEAR data and the 1983/1984 epidemiological studies, several 

logistical decisions were required: 

1. Counts of enterococci reported as 0/100 mL were assigned a log10 value of -1. This assignment 

was made to ensure consistency across marine and freshwaters as this was the approach used in 

the ORD supplied marine water data files. 

2. Non-swimmers were defined as interviewees reporting no water contact. 

3. Swimmers were defined as interviewees reporting immersion in the water. 
5

4. Non-swimmer illness rates were based on all data collected for the beach over the study (illness 

rate per 1000 = number of illnesses among non-swimmers at the beach over the course of the 

study / number of non-swimmers at the beach over the course of the study x 1000. 

5. The highly credible gastrointestinal illness (HCGI) equivalent illness rate was computed as the 

NEEAR study GI (NGI) illness rate divided by a factor of 4.51

.

6. The water quality (for each beach day, season, etc.) was characterized by the geometric mean 

(GM) of the culturable enterococci from all samples collected during the time period (day, 

season, etc.) evaluated. 

7. The seasonal-average illness rate (used for the seasonal evaluation) is: 1000 x (total number of 

illnesses among swimmers for a given beach over the entire study / total number of swimmers at 

the beach during the entire study) – seasonal average non-swimmer illness rate for the beach. 

8. To aggregate data for each beach by days of similar water quality, the following approach was 

used: 

Data for each beach-day were sorted by the observed culturable enterococci geometric 

mean. 

Groups of days with similar culturable enterococci geometric means were established for 

each beach as a first prioritization for aggregates (bins). 

Using the first prioritization described above, aggregates were then constructed to the 

extent possible to contain a similar number of study participants. 

For each bin, the water quality is represented by the geometric mean of enterococci 

densities (CFU/100mL) for study days within the bin (because enterococci is lognormally distributed in water) and the illness rate is the arithmetic mean of all 

illnesses observed for study days within the bin. 

Results 

Aggregation by study day

Tabular results for data aggregated by study day from each of the seven beaches are provided in Tables 1 

through 7. In those tables, the “ill proportion among swimmers”, “ill proportion among non-swimmers”, 

“excess NGI based on daily non-swimmer illness rate”, and “excess NGI based on beach average 

(seasonal) non-swimmer illness rate” were computed based on the other data reported in the Tables. 

Daily excess illness (expressed as HCGI equivalent) based on the beach average non-swimmer illness 

rate2

is plotted against daily the enterococci density geometric mean for NEEAR freshwater and marine 

water study sites in Figures 1 and 2, respectively. 

 

1

 Based on previously mentioned analysis by EPA ORD 

2 The daily average non-swimmer illness rate (also shown in Tables 1-7) is a less robust estimate and is particularly sensitive to 

the daily number of non-swimmers reporting GI illness which is typically small (in many cases <10)
6

Table 1. Huntington Beach 

Beach Dates

Daily geometric mean enterococci density (CFU/100 mL)

1

Total number interviewed

2

Number reporting no water contactNumber reporting immersionNumber reporting NGI, no contactNumber reporting NGI, immersionIll proportion (#/1000) among non-swimmersIll proportion (#/1000) among swimmersExcess NGI, swimmers (#/1000), daily nonswimmer illness rateExcess NGI, swimmers (#/1000), beach average nonswimmer illness rate

HB 8/2/2003 28.9 188 77 76 12 8 155.84 105.26 -50.58 9.50

HB 8/3/2003 66.4 122 88 7 9 1 102.27 142.86 40.58 47.09

HB 8/9/2003 40.4 169 83 53 11 5 132.53 94.34 -38.19 -1.43

HB 8/10/2003 55.4 295 131 100 9 15 68.70 150.00 81.30 54.23

HB 8/16/2003 12.2 183 97 50 10 9 103.09 180.00 76.91 84.23

HB 8/23/2003 7.8 252 143 71 9 11 62.94 154.93 91.99 59.16

HB 8/24/2003 5.2 307 144 105 19 11 131.94 104.76 -27.18 9.00

HB 8/30/2003 290.7 264 165 36 17 7 103.03 194.44 91.41 98.68

HB 8/31/2003 9.6 293 170 80 12 14 70.59 175.00 104.41 79.23

HB 9/6/2003 4.0 158 105 23 7 1 66.67 43.48 -23.19 -52.29

HB 9/7/2003 4.9 266 177 58 17 6 96.05 103.45 7.40 7.68

HB 9/13/2003 11.0 155 77 41 9 5 116.88 121.95 5.07 26.19

HB 9/14/2003 10.3 188 78 57 6 8 76.92 140.35 63.43 44.59

1

 Typically based on 18-27 data points 

2

 Total number interviewed = Number reporting no contact + number reporting immersion + number reporting wading (not shown) 
7

Table 2. West Beach 

Beach Dates

Daily geometric mean enterococci density (CFU/100 mL)

1

Total number interviewed

2

Number reporting no water contactNumber reporting immersionNumber reporting NGI, no contactNumber reporting NGI, immersionIll proportion (#/1000) among nonswimmersIll proportion (#/1000) among swimmersExcess NGI, swimmers (#/1000), daily nonswimmer illness rateExcess NGI, swimmers (#/1000), beach average nonswimmer illness rate

WB 6/1/2003 27.9 43 33 3 2 0 60.61 0.00 -60.61 -49.86

WB 6/7/2003 1.4 186 97 46 6 1 61.86 21.74 -40.12 -28.12

WB 6/8/2003 6.8 58 34 7 0 1 0.00 142.86 142.86 93.00

WB 6/14/2003 1.3 104 66 18 4 1 60.61 55.56 -5.05 5.69

WB 6/15/2003 2.3 172 91 58 4 5 43.96 86.21 42.25 36.35

WB 6/21/2003 0.8 85 37 30 2 7 54.05 233.33 179.28 183.47

WB 6/22/2003 1.0 148 19 112 1 9 52.63 80.36 27.73 30.50

WB 6/28/2003 10.6 66 31 23 0 1 0.00 43.48 43.48 -6.38

WB 6/29/2003 9.5 145 35 84 1 12 28.57 142.86 114.29 93.00

WB 7/4/2003 26.7 139 27 107 2 7 74.07 65.42 -8.65 15.56

WB 7/5/2003 13.6 160 20 114 0 6 0.00 52.63 52.63 2.77

WB 7/6/2003 3.0 134 11 96 0 13 0.00 135.42 135.42 85.56

WB 7/12/2003 1.6 201 25 134 3 19 120.00 141.79 21.79 91.93

WB 7/13/2003 5.6 123 9 99 0 2 0.00 20.20 20.20 -29.66

WB 7/19/2003 1042.1 226 47 135 3 12 63.83 88.89 25.06 39.03

WB 7/20/2003 21.1 281 41 189 4 21 97.56 111.11 13.55 61.25

WB 7/26/2003 37.5 243 27 179 1 28 37.04 156.42 119.39 106.56

WB 7/27/2003 34.5 84 43 30 1 2 23.26 66.67 43.41 16.81

WB 8/2/2003 11.7 174 15 141 1 17 66.67 120.57 53.90 70.71

WB 8/3/2003 3.2 92 14 62 1 5 71.43 80.65 9.22 30.78
8

Table 3. Silver Beach

Beach Dates

Daily geometric mean enterococci density (CFU/100 mL)

1

Total number interviewed

2

Number reporting no water contactNumber reporting immersionNumber reporting NGI, no contactNumber reporting NGI, immersionIll proportion (#/1000) among non-swimmersIll proportion (#/1000) among swimmersExcess NGI, swimmers (#/1000), daily nonswimmer illness rateExcess NGI, swimmers (#/1000), beach average nonswimmer illness rate

SB† 6/26/2004 5.7 409 162 156 10 10 61.73 64.10 2.37 8.38

SB 6/27/2004 11.1 466 115 281 5 18 43.48 64.06 20.58 8.34

SB 7/3/2004 17.3 622 91 402 7 32 76.92 79.60 2.68 23.88

SB 7/4/2004 185.6 325 252 30 5 5 19.84 166.67 146.83 110.95

SB 7/5/2004 14.0 599 296 222 16 17 54.05 76.58 22.52 20.86

SB 7/10/2004 8.5 455 58 334 6 27 103.45 80.84 -22.61 25.12

SB 7/11/2004 24.6 566 75 409 7 31 93.33 75.79 -17.54 20.07

SB 7/17/2004 29.5 618 234 279 14 31 59.83 111.11 51.28 55.39

SB 7/18/2004 50.0 603 204 327 12 22 58.82 67.28 8.45 11.56

SB 7/24/2004 59.5 554 220 190 13 12 59.09 63.16 4.07 7.44

SB 7/25/2004 80.4 474 194 156 10 12 51.55 76.92 25.38 21.20

SB 7/31/2004 104.3 128 104 7 7 0 67.31 0.00 -67.31 -55.72

SB 8/1/2004 47.2 483 76 345 2 35 26.32 101.45 75.13 45.73

SB 8/7/2004 20.8 729 252 359 15 18 59.52 50.14 -9.38 -5.58

SB 8/8/2004 17.9 516 101 310 8 22 79.21 70.97 -8.24 15.25

SB 8/14/2004 55.5 383 138 173 10 14 72.46 80.92 8.46 25.20

SB 8/15/2004 45.5 502 170 246 9 15 52.94 60.98 8.03 5.26

SB 8/21/2004 101.4 443 119 259 3 15 25.21 57.92 32.70 2.19

SB 8/22/2004 22.9 469 243 142 13 18 53.50 126.76 73.26 71.04

SB 9/3/2004 28.3 185 35 116 2 7 57.14 60.34 3.20 4.62

SB 9/4/2004 30.3 561 61 415 3 33 49.18 79.52 30.34 23.80

SB 9/5/2004 127.0 484 96 318 3 28 31.25 88.05 56.80 32.33

SB 9/6/2004 73.1 298 78 175 8 8 102.56 45.71 -56.85 -10.01
9

Table 4. Washington Park Beach

Beach Dates

Daily geometric mean enterococci density (CFU/100 mL)

1

Total number interviewed

2

Number reporting no water contactNumber reporting immersionNumber reporting NGI, no contactNumber reporting NGI, immersionIll proportion (#/1000) among non-swimmersIll proportion (#/1000) among swimmersExcess NGI, swimmers (#/1000), daily nonswimmer illness rateExcess NGI, swimmers (#/1000), beach average nonswimmer illness rate

WP 6/26/2004 8.36 235 98 93 6 4 61.22 43.01 -18.21 -19.84

WP 6/27/2004 9.18 251 72 124 7 15 97.22 120.97 23.75 58.12

WP 7/3/2004 17.9 188 49 104 4 11 81.63 105.77 24.14 42.92

WP 7/4/2004 15.4 187 52 105 3 7 57.69 66.67 8.97 3.82

WP 7/5/2004 95 371 148 167 8 13 54.05 77.84 23.79 15.00

WP 7/10/2004 37.5 215 39 144 3 18 76.92 125.00 48.08 62.15

WP 7/11/2004 27.6 184 48 110 5 10 104.17 90.91 -13.26 28.06

WP 7/17/2004 30.1 172 46 96 4 6 86.96 62.50 -24.46 -0.35

WP 7/18/2004 43.0 177 72 87 4 8 55.56 91.95 36.40 29.11

WP 7/24/2004 35.2 154 81 49 4 12 49.38 244.90 195.52 182.05

WP 7/25/2004 26.0 209 89 83 3 7 33.71 84.34 50.63 21.49

WP 8/1/2004 7.61 236 28 181 2 11 71.43 60.77 -10.66 -2.07

WP 8/7/2004 43.0 234 69 121 6 10 86.96 82.64 -4.31 19.80

WP 8/8/2004 28.8 276 40 181 3 14 75.00 77.35 2.35 14.50

WP 8/14/2004 39.9 78 42 10 1 0 23.81 0.00 -23.81 -62.85

WP 8/15/2004 37.4 236 73 132 5 10 68.49 75.76 7.26 12.91

WP 8/21/2004 24.9 169 65 84 1 7 15.38 83.33 67.95 20.49

WP 8/22/2004 22.2 176 33 104 1 9 30.30 86.54 56.24 23.69

WP 9/3/2004 25.7 14 4 8 1 0 250.00 0.00 -250.00 -62.85

WP 9/4/2004 14.4 238 37 175 2 18 54.05 102.86 48.80 40.01

WP 9/5/2004 28.4 266 53 165 3 11 56.60 66.67 10.06 3.82

WP 9/6/2004 32.8 78 19 37 3 5 157.89 135.14 -22.76 72.29
10

Table 5. Edgewater Beach

Beach Dates

Daily geometric mean enterococci

density 

(CFU/100 mL)

1

Total number interviewed

2

Number reporting no water contactNumber reporting immersionNumber reporting NGI, no contactNumber reporting NGI, immersionIll proportion (#/1000) among non-swimmersIll proportion (#/1000) among swimmersExcess NGI, swimmers (#/1000), daily nonswimmer illness rateExcess NGI, swimmers (#/1000), beach average nonswimmer illness rate

EB 6/4/2005 23.77 75 24 27 0 7 0.0 259.3 259.3 175.0

EB 6/5/2005 16.76 58 28 13 3 2 107.1 153.8 46.7 69.6

EB 6/18/2005 68.06 44 16 6 1 0 62.5 0.0 -62.5 -84.2

EB 6/19/2005 15.34 102 37 37 4 4 108.1 108.1 0.0 23.9

EB 6/25/2005 12.01 68 15 31 0 3 0.0 96.8 96.8 12.6

EB 6/26/2005 3.08 79 15 33 0 2 0.0 60.6 60.6 -23.6

EB 7/2/2005 22.66 67 23 22 2 4 87.0 181.8 94.9 97.6

EB 7/3/2005 7.77 105 28 24 5 5 178.6 208.3 29.8 124.1

EB 7/4/2005 17.09 92 32 27 4 1 125.0 37.0 -88.0 -47.2

EB 7/16/2005 88.75 64 11 34 1 5 90.9 147.1 56.1 62.8

EB 7/17/2005 3.86 40 17 6 1 0 58.8 0.0 -58.8 -84.2

EB 7/23/2005 10.78 66 23 22 2 2 87.0 90.9 4.0 6.7

EB 7/24/2005 3.91 52 17 20 1 0 58.8 0.0 -58.8 -84.2

EB 7/30/2005 0.66 98 21 34 1 2 47.6 58.8 11.2 -25.4

EB 7/31/2005 1.37 79 20 13 5 2 250.0 153.8 -96.2 69.6

EB 8/6/2005 19.36 47 8 13 0 1 0.0 76.9 76.9 -7.3

EB 8/7/2005 4.10 49 13 21 0 3 0.0 142.9 142.9 58.6

EB 8/13/2005 2.05 58 14 14 0 1 0.0 71.4 71.4 -12.8

EB 8/14/2005 2.50 38 8 11 1 3 125.0 272.7 147.7 188.5

EB 8/20/2005 1.20 28 9 9 0 0 0.0 0.0 0.0 -84.2

EB 8/21/2005 4.05 34 1 12 1 0 1000.0 0.0 -1000.0 -84.2
11

Table 6. Fairhope Beach

Beach Dates

Daily geometric mean enterococcidensity (CFU/100 mL)

1

Total number interviewed

2

Number reporting no water contactNumber reporting immersionNumber reporting NGI, no contactNumber reporting NGI, immersionIll proportion (#/1000) among non-swimmersIll proportion (#/1000) among swimmersExcess NGI, swimmers (#/1000), daily nonswimmer illness rateExcess NGI, swimmers (#/1000), beach average nonswimmer illness rate

FB† 5/19/2007 15.07 154 85 33 8 1 94.12 30.30 -63.81 -56.45

FB 5/20/2007 2.69 183 98 44 12 3 122.45 68.18 -54.27 -18.57

FB 5/25/2007 6.71 81 47 11 4 0 85.11 0.00 -85.11 -86.75

FB 5/26/2007 8.43 145 64 50 3 2 46.88 40.00 -6.88 -46.75

FB 5/27/2007 13.80 126 28 54 2 5 71.43 92.59 21.16 5.84

FB 5/28/2007 13.76 100 35 30 6 2 171.43 66.67 -104.76 -20.09

FB 6/2/2007 230.10 106 48 37 4 3 83.33 81.08 -2.25 -5.67

FB 6/3/2007 27.05 73 26 16 2 2 76.92 125.00 48.08 38.25

FB 6/9/2007 25.41 64 28 17 1 2 35.71 117.65 81.93 30.89

FB 6/10/2007 18.88 99 28 43 1 1 35.71 23.26 -12.46 -63.50

FB 6/16/2007 78.55 110 46 44 3 8 65.22 181.82 116.60 95.07

FB 6/17/2007 143.73 104 57 24 4 0 70.18 0.00 -70.18 -86.75

FB 6/23/2007 23.00 66 22 27 1 3 45.45 111.11 65.66 24.36

FB 6/24/2007 76.43 57 22 19 5 5 227.27 263.16 35.89 176.41

FB 6/30/2007 27.44 49 22 11 0 3 0.00 272.73 272.73 185.97

FB 7/1/2007 10.02 71 22 34 2 7 90.91 205.88 114.97 119.13

FB 7/4/2007 45.61 97 39 37 4 4 102.56 108.11 5.54 21.36

FB 7/7/2007 10.45 43 12 16 0 2 0.00 125.00 125.00 38.25

FB 7/8/2007 48.85 78 28 34 1 0 35.71 0.00 -35.71 -86.75

FB 7/14/2007 70.22 50 19 22 1 1 52.63 45.45 -7.18 -41.30

FB 7/15/2007 59.71 27 7 8 1 1 142.86 125.00 -17.86 38.25

FB 7/21/2007 12.20 25 11 8 1 0 90.91 0.00 -90.91 -86.75

FB 7/22/2007 6.88 55 28 11 4 4 142.86 363.64 220.78 276.88

FB 7/28/2007 14.59 22 7 11 0 3 0.00 272.73 272.73 185.97

FB 7/29/2007 4.72 30 24 4 4 0 166.67 0.00 -166.67 -86.75
12

Table 7. Goddard Beach

Beach Dates

Daily geometric mean enterococci density (CFU/100 mL)

1

Total number interviewed

2

Number reporting no water contactNumber reporting immersionNumber reporting NGI, no contactNumber reporting NGI, immersionIll proportion (#/1000) among nonswimmersIll proportion (#/1000) among swimmersExcess NGI, swimmers (#/1000), daily nonswimmer illness rateExcess NGI, swimmers (#/1000), beach average nonswimmer illness rate

GB 6/23/2007 3.26 160 98 21 4 0 40.82 0.00 -40.82 -46.09

GB 6/24/2007 1.03 170 105 28 4 3 38.10 107.14 69.05 61.06

GB 6/30/2007 1.29 119 64 25 5 2 78.13 80.00 1.88 33.91

GB 7/1/2007 6.29 156 108 19 3 2 27.78 105.26 77.49 59.18

GB 7/4/2007 4.90 200 118 54 5 1 42.37 18.52 -23.85 -27.57

GB 7/7/2007 4.29 135 63 31 0 0 0.00 0.00 0.00 -46.09

GB 7/8/2007 0.71 184 58 95 1 3 17.24 31.58 14.34 -14.51

GB 7/14/2007 1.95 151 65 48 0 4 0.00 83.33 83.33 37.25

GB 7/15/2007 0.61 162 64 61 5 7 78.13 114.75 36.63 68.67

GB 7/21/2007 4.89 74 49 9 2 0 40.82 0.00 -40.82 -46.09

GB 7/22/2007 2.32 146 83 38 5 4 60.24 105.26 45.02 59.18

GB 7/28/2007 4.83 90 35 40 0 1 0.00 25.00 25.00 -21.09

GB 7/29/2007 2.94 63 31 12 1 0 32.26 0.00 -32.26 -46.09

GB 8/4/2007 10.23 144 34 79 0 8 0.00 101.27 101.27 55.18

GB 8/5/2007 22.95 156 72 53 5 4 69.44 75.47 6.03 29.39

GB 8/11/2007 2.88 81 42 16 4 0 95.24 0.00 -95.24 -46.09

GB 8/12/2007 2.26 101 36 33 3 3 83.33 90.91 7.58 44.82

GB 8/18/2007 2.91 87 64 8 1 0 15.63 0.00 -15.63 -46.09

GB 8/19/2007 3.05 77 67 3 5 0 74.63 0.00 -74.63 -46.09

GB 8/25/2007 3.28 73 21 27 1 0 47.62 0.00 -47.62 -46.09

GB 8/26/2007 1.78 103 71 23 4 2 56.34 86.96 30.62 40.87

GB 9/1/2007 38.72 65 57 3 3 0 52.63 0.00 -52.63 -46.09

GB 9/2/2007 6.32 101 80 5 5 1 62.50 200.00 137.50 153.91

GB 9/3/2007 13.66 170 99 48 7 3 70.71 62.50 -8.21 16.41
13

Figure 1. Daily excess HCGI vs. daily Enterococcus density geometric mean for NEEAR freshwater 

beaches. 

HCGI assumed equal to NGI rate / 4.5. 

Excess illness rate is calculated as illness rate among swimmers reporting immersion minus the average illness rate among nonswimmers (reporting no contact) for the beach over the entire study period. 

Figure 2. Daily excess HCGI vs. daily Enterococcus density geometric mean for NEEAR temperate 

POTW-impacted marine beaches. 

HCGI assumed equal to NGI rate / 4.5. 

Excess illness rate on each beach day calculated as illness rate among swimmers reporting immersion minus the average illness 

rate among non-swimmers (reporting no contact) for the beach over the entire study period. 
14

Aggregation by season

Tabular results for data aggregated by season from each of the seven beaches are provided in Table 8. 

Seasonal average excess illness (expressed as NGI/4.5 = HCGI equivalent) is plotted against seasonal 

average Enterococcus density geometric mean for NEEAR freshwater and marine water study sites in 

Figures 3 and 4, respectively. 

Table 8. Seasonal average water quality and illness rates for NEEAR beaches 

Beach

Water 

quality Participant breakdown

NGI 

(#)

NGI rate 

(# / 1000)

Excess 

illness rate 

(#/1000) 

(illness rate -

nonswimmer 

illness rate)

Seasonal GM ENT (CFU/100 mL)All samplesTotal # interviewedNo water contactSwimmers (immersion reported)No contactImmersionNo contactImmersionExcess NGI / 1000Excess HCGI equivalent, /1000

Fresh

Huntington 

Beach 17.5 2840 1535 757 147 101 95.8 133.4 37.7 8.4

West Beach 7.9 2865 722 1668 36 170 49.9 101.9 52.1 11.6

Silver 

Beach 33.1 10872 3374 5651 188 430 55.7 76.1 20.4 4.5

Washington 

Park Beach 27.7 4344 1257 2360 79 206 62.8 87.3 24.4 5.4

Marine

Edgewater 

Beach

7.3 1343 380 429 32 47 84.2 109.6 25.3 5.6

Fairhope 

Beach 22.1 2015 853 645 74 62 86.8 96.1 9.4 2.1

Goddard 

Beach 3.6 2968 1584 779 73 48 46.1 61.6 15.5 3.4

Excess illness rate based on season-average non-swimmer illness rate at each beach to ensure that small sample sizes 

of non-swimmer illness rate do not bias excess illness from swimming. 

Use of daily illness rate among non-swimmers to determine daily excess illness rate was assessed but not reported. 
15

Log10 Enterococci density / 100mL

0.0 0.5 1.0 1.5 2.0 2.5 3.0

HCGI rate /1000 swimmers

0

5

10

15

20

25

30

35

40

1986 freshwater seasonal avg

1986 freshwater regression

NEEAR freshwater beach seasonal avg

Figure 3. Seasonal average freshwater NEEAR study data and 1986 freshwater study data (season 

averages). 

Log10 Enterococci density / 100mL

0.0 0.5 1.0 1.5 2.0 2.5 3.0

HCGI rate / 1000 swimmers

0

5

10

15

20

25

30

35

40

1986 beach seasonal avg

1986 marine water regression

NEEAR marine beach seasonal avg

Figure 4. Seasonal average marine NEEAR study data and 1986 marine water study data (season 

averages). 

Aggregation by study days of similar culturable enterococci

Tabular results for data aggregated by days of similar culturable enterococci from each of the seven 

beaches are provided in Table 9. As illustrated in Table 9, aggregation as described previously generally 

resulted in four bins per beach (with typically 3 to 7 days per bin). Silver Beach had to be split into five 

bins because of the heterogeneity of the observations with reported densities above 30 cfu/100mL, and 

Goddard Beach was split into two bins because most observations (20/24) had very low reported 

enterococci densities (<7 cfu/100mL). Average excess illness rate (expressed as HCGI equivalent) is 

plotted against enterococci density geometric mean for NEEAR freshwater and marine water study sites 

aggregated by study days of similar culturable enterococci in Figures 5 and 6, respectively. 
16

Table 9. Average water quality and illness rates for NEEAR data aggregated by days of similar 

water quality 

B each B in 

Daily geometric 

mean 

E nterococcus 

density 

(C F U/100 mL )

T otal number 

interviewed

Number 

reporting no 

water contact

Number 

reporting 

immersion

NG I, no 

contact

NG I, 

immersion

NG I 

proportion 

(#/1000) 

among nonswimmers

NG I 

proportion 

(#/1000) 

among 

swimmers

E xcess NG I 

swimmers 

(#/1000), 

beach 

average 

nonswimmer 

illness rate

E xcess HC G I 

swimmers 

(#/1000), beach 

average 

nonswimmer 

illness rate

H B B in 1 4.7 731 426 186 43 18 100.9 96.8 1.0 0.2

H B B in 2 9.2 733 391 208 27 33 69.1 158.7 62.9 14.0

H B B in 3 15.7 526 251 167 31 22 123.5 131.7 35.9 8.0

H B B in 4 81.1 850 467 196 46 28 98.5 142.9 47.1 10.5

B each B in 

Daily geometric mean 

E nterococcus 

density 

(C F U/100 mL )

T otal number 

interviewed

Number 

reporting no 

water contact

Number 

reporting 

immersion

NG I, no 

contact

NG I, 

immersion

NG I 

proportion 

(#/1000) 

among nonswimmers

NG I 

proportion 

(#/1000) 

among 

swimmers

E xcess NG I 

swimmers 

(#/1000), beach 

average 

nonswimmer 

illness rate

E xcess HC G I 

swimmers 

(#/1000), beach 

average 

nonswimmer 

illness rate W B B in 1 1.6 1122 360 556 21 6 0 58.3 107.9 58.0 12.9 W B B in 2 9.2 726 144 468 2 3 9 13.9 83.3 33.4 7.4 W B B in 3 25.1 463 101 299 8 2 8 79.2 93.6 43.7 9.7 W B B in 4 110.4 553 117 344 5 4 2 42.7 122.1 72.2 16.0

B each B in 

Daily geometric 

mean 

E nterococcus 

density 

(C F U/100 mL )

T otal number 

interviewed

Number 

reporting no 

water contact

Number 

reporting 

immersion

NG I, no 

contact

NG I, 

immersion

NG I 

proportion 

(#/1000) 

among nonswimmers

NG I 

proportion 

(#/1000) 

among 

swimmers

E xcess NG I 

swimmers 

(#/1000), 

beach 

average 

nonswimmer 

illness rate

E xcess HC G I 

swimmers 

(#/1000), 

beach 

average 

nonswimmer 

illness rate

S B B in 1 7.0 864 220 490 16 37 72.7 75.5 19.8 4.4

S B B in 2 14.8 2203 603 1215 36 89 59.7 73.3 17.6 3.9

S B B in 3 25.8 3128 900 1720 54 138 60.0 80.2 24.5 5.5

S B B in 4 51.3 2525 808 1281 46 98 56.9 76.5 20.8 4.6

S B B in 5 106.6 2152 843 945 36 68 42.7 72.0 16.3 3.6

B each B in 

Daily geometric mean 

E nterococcus 

density (C F U/100 

mL )

T otal number 

interviewed

Number 

reporting no 

water contact

Number 

reporting 

immersion

NG I, no 

contact

NG I, 

immersion

NG I proportion 

(#/1000) 

among nonswimmers

NG I 

proportion 

(#/1000) 

among 

swimmers

E xcess NG I 

swimmers 

(#/1000), beach 

average 

nonswimmer 

illness rate

E xcess HC G I 

swimmers 

(#/1000), beach 

average 

nonswimmer 

illness rate W P B in 1 8.4 722 198 398 15 3 0 75.8 75.4 12.6 2.8 W P B in 2 17.2 789 171 488 10 4 5 58.5 92.2 29.4 6.5 W P B in 3 27.9 1368 364 764 23 6 0 63.2 78.5 15.7 3.5 W P B in 4 44.6 1465 524 710 31 7 1 59.2 100.0 37.2 8.3

B each B in 

Daily geometric mean 

E nterococcus density 

(C F U/100 mL )

T otal number 

interviewed

Number 

reporting no 

water 

contact

Number 

reporting 

immersion

NG I, no 

contact

NG I, 

immersion

NG I 

proportion 

(#/1000) 

among nonswimmers

NG I 

proportion 

(#/1000) 

among 

swimmers

E xcess NG I, 

swimmers 

(#/1000), beach 

average 

nonswimmer 

illness rate

E xcess HC G I 

swimmers 

(#/1000), 

beach 

average 

nonswimmer 

illness rate

E B B in 1 2.31 555 135 173 10 1 3 74.1 75.1 -9.1 -2.0

E B B in 2 10.0 239 66 77 7 1 0 106.1 129.9 45.7 10.1

E B B in 3 18.9 441 152 139 13 1 9 85.5 136.7 52.5 11.7

E B B in 4 77.7 108 27 40 2 5 74.1 125.0 40.8 9.1

B each B in 

Daily 

geometric 

mean 

E nterococcu

s density 

(C F U/100 

mL )

T otal number 

interviewed

Number 

reporting no 

water contact

Number 

reporting 

immersion

NG I, no 

contact

NG I, 

immersion

NG I proportion 

(#/1000) 

among nonswimmers

NG I 

proportion 

(#/1000) 

among 

swimmers

E xcess NG I, 

swimmers 

(#/1000), 

beach 

average 

nonswimmer 

illness rate

E xcess HC G I 

swimmers 

(#/1000), beach 

average 

nonswimmer 

illness rate

F B B in 1 5.5 494 261 120 27 9 103.4 75.0 -11.8 -2.6

F B B in 2 12.7 541 200 186 19 20 95.0 107.5 20.7 4.6

F B B in 3 24.1 351 126 114 5 1 1 39.7 96.5 9.7 2.2

F B B in 4 81.0 629 266 225 23 22 86.5 97.8 11.0 2.4

B each B in 

Daily 

geometric 

mean 

E nterococcu

s density 

(C F U/100 

mL )

T otal number 

interviewed

Number 

reporting no 

water contact

Number 

reporting 

immersion

NG I, no 

contact

NG I, 

immersion

NG I proportion 

(#/1000) 

among nonswimmers

NG I 

proportion 

(#/1000) 

among 

swimmers

E xcess NG I, 

swimmers 

(#/1000), 

beach 

average 

nonswimmer 

illness rate

E xcess HC G I 

swimmers 

(#/1000), beach 

average 

nonswimmer 

illness rate

G B B in 1 2.6 2433 1322 596 58 33 43.9 55.4 9.3 2.1

G B B in 2 18.8 535 262 183 15 15 57.3 82.0 35.9 8.0
17

Log10 Enterococci density / 100mL

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

HCGI rate /1000 swimmers

0

5

10

15

20

25

30

35

40

Figure 5 Freshwater NEEAR data aggregated by similar water quality and 1986 freshwater data 

(season averages). 

NEEAR study data presented as colored symbols (West Beach green, Huntington Beach red, Silver Beach blue, 

Washington Park yellow), 

1986 freshwater study data presented as black circles, 

1986 freshwater study regression presented as solid line.

Log10 Enterococci density / 100mL

0.0 0.5 1.0 1.5 2.0 2.5 3.0

HCGI rate / 1000 swimmers

-5

0

5

10

15

20

25

30

35

40

Figure 6 Marine NEEAR data aggregated by similar water quality and 1986 marine water study 

data (season averages). 

NEEAR study data presented as colored symbols (Edgewater green, Fairhope red, Goddard blue), 

1986 marine water study data presented as black circles, 

1986 marine water study regression presented as solid line regression presented as solid line
18

Interpretation of Results 

NEEAR study daily geometric mean culturable enterococci were highly variable in both marine and 

freshwaters (Refer to Figures 1 and 2). Previously reported epidemiological results (Wade et al., 2008) 

indicate that in freshwater, swimmers exposed to waters with culturable enterococci levels above the 

AWQC values had higher risks than non-swimmers or swimmers exposed below this value. Direct 

comparison of daily data to the epidemiological results from the 1980s was not possible because daily 

data were not available from the 1980s studies. 

In comparing the seasonal average freshwater NEEAR study data with the 1986 freshwater study data 

(Figure 3), three of four points appear consistent, whereas one data point (West Beach) is divergent from 

the rest of the data. Culturable enterococci data from the NEEAR marine water studies were in the same 

range as the marine water quality data from the 1980s (Figure 4). However, the GI illness rates from the 

NEEAR marine water studies appear to be at the low end or slightly lower than those from the marine 

water epidemiology studies conducted in the 1980s. 

When data aggregated by days of similar culturable enterococci from each of the seven beaches are 

compared to the water quality and epidemiology data from the 1980s (Figures 5 and 6), several interesting 

observations emerge: 1) Most of the data from freshwater beaches are relatively consistent with the data 

from the 1980s (the observed health effects fall in the expected range based on culturable enterococci 

levels), 2) One data point from West Beach and one data point from Huntington Beach deviate from all 

other NEEAR data and data from the 1980s (low observed enterococci levels and high adverse health 

effects rates). These data points could be of particular concern because they represent conditions in 

which culturable enterococci levels are low (<10cfu/100mL), yet observed GI illness rates are relatively 

high (>12 HCGI/1000 events), 3) data from marine water beaches are relatively consistent with the water 

quality data and observed GI illness trends from the 1980s except that the observed levels of GI illness are 

generally at the lower end of that observed during the studies from the 1980s. 

To further evaluate the potential underlying nature of the divergent data points identified above (Figure 

5), we evaluated ancillary data in the provided data tables provided by ORD (antecedent rainfall, wind, 

tides, etc.) to determine if trends existed related to low enterococci densities and high adverse health 

effect levels. However, no obvious explanation was revealed for the low enterococci densities and high 

adverse health effect levels. We then investigated whether qPCR enterococci performed similarly to 

culturable enterococci. To facilitate this comparison, we plotted the geometric mean of the qPCR 

enterococci densities (CCE/100mL) for study days within the bin against the arithmetic mean illness rate 

for study days within the bin (the bins were not changed, and thus represent days of low, moderately low, 

moderately high, or high culturable enterococci). Those results are presented for NEEAR freshwater and 

marine beaches in Figures 7 and 8, respectfully. The combined results for NEEAR freshwater and marine 

beaches together are presented in Figure 9. Inspection of the data presented in Figures 7 through 9 clearly 

indicate that the qPCR densities (of the data aggregated by days of similar water quality) generally 

increased with increasing rates of GI illness and do not contain divergent points from this general trend 

(in contrast to culturable enterococci as illustrated in Figure 5). This finding could be of particular 

interest and could provide previously unavailable insights for public health protection for conditions at 
19

specific beaches where culturable enterococci densities are observed to be low while qPCR densities are 

substantially higher. 

Log10 Enterococci density CCE / 100mL

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

HCGI rate /1000 swimmers

0

5

10

15

20

Figure 7 Freshwater NEEAR qPCR results binned by days of similar culturable enterococci 

(West Beach green, Huntington Beach red, Silver Beach blue, Washington Park yellow) 

Log10 Enterococci density CCE / 100mL

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

HCGI rate / 1000 swimmers

0

5

10

15

20

Figure 8 Marine water NEEAR qPCR results binned by days of similar culturable enterococci 

Edgewater green, Fairhope red, Goddard blue 
20

Log10 Enterococci density CCE / 100mL

0 1 2 3

HCGI rate /1000 swimmers

0

5

10

15

20

Figure 9 Combined Freshwater and Marine NEEAR qPCR results binned by days similar 

culturable enterococci 

West Beach green, Huntington Beach red, Silver Beach blue, Washington Park yellow, Edgewater grey 

square, Fairhope grey triangle, Goddard grey circle 

Conclusions 

The POTW-impacted NEEAR study culturable enterococci data are generally consistent with the data 

from the 1980s for culturable enterococci and observed excess GI illness. When the daily NEEAR data 

were aggregated by days of similar culturable enterococci, there were several conditions (freshwater 

beaches with low enterococci density and relatively high excess illness) that deviated from the rest of the 

results. Subsequent investigation indicated that, in contrast to culturable enterococci, qPCR enterococci 

densities (of the aggregated data) generally increased with increasing rates of GI illness. This observation 

indicates that at select sites and under specific conditions the qPCR enterococci density may better 

correspond to adverse health effect levels than culturable enterococci.

References

Cabelli, V.J. (1983) Health effects criteria for marine recreational waters. USEPA Cincinnati, OH. 

Dufour, A. (1984) Health effects criteria for fresh recreational waters. US EPA Cincinnati, OH. 

U.S. EPA (1986) Ambient water quality criteria for bacteria, Office of Water, EPA440/5-84-

002,Washington, DC, 

Wade, T.J., Calderon, R.L., Sams, E., Beach, M., Brenner, K.P., Williams, A.H., and Dufour, A.P. (2006) 

Rapidly measured indicators of recreational water quality are predictive of swimming-associated 

gastrointestinal illness. Environ Health Perspect 114(1): 24-28. 
21

Wade, T.J., Calderon, R.L., Brenner, K.P., Sams, E., Beach, M., Haugland, R., Wymer, L., and Dufour, 

A.P. (2008) High sensitivity of children to swimming-associated gastrointestinal illness: results using a 

rapid assay of recreational water quality. Epidemiology 19(3): 375-383. 

Wade, T.J., Sams, E., Brenner, K.P., Haugland, R., Chern, E., Beach, M., Wymer, L., Rankin, C.C., Love, 

D., Li, Q., Noble, R., and Dufour, A.P. (2010) Rapidly measured indicators of recreational water quality 

and swimming-associated illness at marine beaches: A prospective cohort study. Environ Health 9(1): 66.