Conservation practices and produce food safetyin California

Rob Atwill, D.V.M., Ph.D.University of California-Davis

Reported annual foodborne illness in USA, CDC, 20139.4 million illnesses, 55,961 hospitalizations, 1351 deaths

Bacterial Chemical Parasitic Viral

Fish & shellfish 4% 62% 33% 4%

Dairy, egg, meat 64% 13% 0.1% 30%

Produce 27% 19% 30% 60%

TOTAL 3.6 250 230 5.5million thousand thousand million

Reported annual foodborne illness in USA, CDC, 20139.4 million illnesses, 55,961 hospitalizations, 1351 deaths

Bacterial Chemical Parasitic Viral

Fish & shellfish 4% 62% 33% 4%

Dairy, egg, meat 64% 13% 0.1% 30%

Produce 27% 19% 30% 60%

TOTAL 3.6 250 230 5.5million thousand thousand million

leafy greens tomatoes cantaloupeFoods eatenraw at risk

Fall 2006 spinach outbreak of E. coli O157:H7Product originated from a field in San Benito County, CA

Outbreak in late Aug to early September

Are these produce outbreaks the result of irrigation water, winter runoff, livestock grazing and/or wildlife?

What is the source and process of connectivity?

Microbiological safety of irrigation water

E. coli concentrations in California irrigation water(industry data, 2/2007 to 11/2010, n=44,000)

77%

11% 8%

2%1% 0.8%

0.1%

0.5% 0.4%

0%

20%

40%

60%

80%

100%

1

10

100

1,000

10,000

100,000

Prop

ortio

n

Freq

uenc

y

E. coli concentration (MPN/100mL)0 1-5 6-25 26-50 51-100 101-200 201-235 236-567 >567

Microbiological safety of irrigation reservoirsand tailwater ponds (sediment basins)

E. coli concentrations (MPN/100mL)

Seasons Well Reservoir Difference % Increase

Winter 1.0 18.5 17.5 >1800Spring 9.8 21.5 11.7 >200

Summer 19.4 77.6 58.2 400Fall 20.8 65.4 44.6 >300

Overall 13.9 50.6 36.7 >300

Changes in water quality: well to surface storagecentral coastal California, 2/2007 – 11/2010

Data reproduced from Atwill, 2011

9

Fencing to exclude fecal deposition by terrestrial wildlife

Chemical treatments

Dewater in fall, dry out the sediments

Removal

Other ideas

Key processes driving waterborne pathogen transmission

A. Vertebrate pathogen loading: domestic and wild populationsB. Hydrological transport: linking fecal sources with waterC. Inactivation kinetics: survival during transport

CA data: rangeland buffers can retain >95%of key pathogens in winter and spring;

>99.9% achievable under certain conditions

Herd pos n prev (%)A 0 489 0.0B 7 480 1.5C 0 200 0.0D 44 434 10.1E 0 61 0.0F 6 386 1.6G 2 271 0.7H 9 256 3.5Total 68 2715 2.5

Cow-calf herds, central coastal CA, 2008-2010E. coli O157 infection ranged from 0% to 10%

Key focus: pathogen sources and modes of transport

Irrigation water, proximity to livestock, rangeland runoff, wildlife intrusion, soil amendments

Runoff in winter, outbreaks in late summer/fall?

Longitudinal survey, 4/2008 to 11/2011Soil samples 0.4% (10/2450)Produce samples 0.0% ( 0/2462)Water samples 0.4% ( 1/242)Livestock 2.5% (68/2715)

Key focus: pathogen sources and modes of transport

Irrigation water, proximity to livestock, rangeland runoff, wildlife intrusion, soil amendments

Runoff in winter, outbreaks in late summer/fall?

Longitudinal survey, 4/2008 to 11/2011Soil samples 0.4% (10/2450)Produce samples 0.0% ( 0/2462)Water samples 0.4% ( 1/242)Livestock 2.5% (68/2715)

E. coli O157:H7, 2008-10Feral pig 10/200 (5%)Coyote 2/95 (2%)Am. crow 5/93 (5%)Cowbird 2/60 (3%)Rabbit 0/108 (0%)Skunk 0/63 (0%)Blackbird 0/112 (0%)Raccoon 0/28 (0%)

Beef cattle 68/2715 (2.5%)

Clarify sources of Ec O157and we can better design:• fencing style• modify specific habitat• target specific wildlife

E. coli O157:H7 in wildlifeand cattle

Rodent species Cryptosporidium Giardia

CA parasitic mouse 11% 13%Deer mouse 33% 27%Dusky-footed wood rat 17% 17%

TOTAL 28% 25%

Prevalence of pathogens in wild rodents in produce production fields, central California

Preliminary data: Crypto appears human infectious, Giardia mostly not

E. coli O157:H7 2/1,043 (0.2%)Salmonella 30/1,043 (2.9%)

When wildlife congregate then food safety risks are magnified

Randomized field trials of romaine lettuce Salinas Valley, 2011 & 2012

scat

BED BED

FUR

RO

W

20 to 30% of nearby heads of lettucecontaminated with E. coli O157:H7

Add in 2 hours of irrigation

0

1

100

10,000

1,000,000

10 15 20 25Distance between lettuce and scat (inches)

E. c

oli O

157:

H7

/ hea

d le

ttuc

eE. coli O157:H7 per head of Romaine lettuce

10

100

1,000

10,000

100,000

0 10 20 30 40 50 60 70 80

Age of scat (hrs) prior to irrigation

E. c

oli O

157:

H7

/ hea

d le

ttuc

eE. coli O157:H7 per head of Romaine lettuce

Animal intrusion <24 hrs prior

Drip irrigation versus overhead sprinklerregarding fecal splash

Exclude wildlife by fencing, trappingand habitat modification,

dust abatement

Vegetative or Bare Ground Buffers

• Bare ground may reduce food and cover for some rodents.• Con: eliminates pathogen reduction benefits of vegetation.• Con: causes soil erosion & sedimentation.• Con: degrades water quality & aquatic habitat.

Daniel Mountjoy, NRCS

Vegetative Conservation Practice in Question: Grassed Waterways

• Pro: Convey runoff without causing erosion or flooding.

• Pro: Reduce gulley erosion.• Pro: Protect and improve water

quality.• Pro: Can be mowed and

maintained to discourage rodents.• Con: Considered by some as

possible cover for rodents or amphibians (foreign object concern).

Daniel Mountjoy, NRCS

Benefits to food safety versus costs to conservation

Questions?