United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture 

Veterinary Services 

Centers for Epidemiology and Animal Health March 2011 

_________________________________________________________________________________________________________________________ 

Prevalence of Coxiella burnetii in 

Bulk-tank Milk on U.S. Dairy 

Operations, 2007 

Background 

Coxiella burnetii is the bacterium that causes Q fever in 

animals and humans and is found throughout most of 

the world. While most animals, including domestic cats 

and dogs and wild animals, can become infected with 

C. burnetii, cattle, sheep, and goats are considered the 

most important domestic reservoirs of the bacteria.1 2 3 

Although animals infected with C. burnetii often show no 

clinical signs, the organism can cause abortions in 

sheep and goats. 

Importantly, C. burnetii can be transmitted from 

animals to humans. Symptoms of infection in humans 

vary from unapparent to severe. Some human cases 

cause mild flu-like symptoms such as headache, fever, 

and muscle aches, which usually resolve without 

treatment. For people with chronic C. burnetii infections, 

the liver and heart are usually affected.1 

C. burnetii is highly infectious and spreads mainly 

through inhalation of bacteria shed via the placenta, 

amniotic fluid, and feces of infected animals. Ticks and 

consumption of raw infected animal products are also 

suspected modes of transmission. Because C. burnetii 

localizes in the mammary gland raw dairy products have 

been associated with animal-to-human transmission.1 2 3 

High temperature, short-time pasteurization standards 

(71.7°C for 15 seconds) in the United States have been 

developed to inactivate C. burnetii in milk.4 The Centers 

for Disease Control and Prevention recommend the 

consumption of only pasteurized milk and milk products 

to prevent C. burnetii infection5 

Animals infected with C. burnetii may clear the 

infection or remain infected for life. Shedding of 

C. burnetii in milk ranges from sporadic to persistent, 

suggesting that at least some animals are infected for an 

extended period.6 In addition, a U.S. study reported a 

positive association among dairy cows that tested 

positive for C. burnetii and chronic subclinical mastitis, 

as measured by somatic cell counts.7

 

The prevalence of C. burnetii in bulk-tank milk from 

dairy cattle in England and Wales was reported at 21 

percent.8

 A U.S. study found Coxiella antibodies in 22 of 

24 veterinary-school-associated dairy herds,9 while 

another study of primarily Northeast dairy herds reported 

a herd-level prevalence of more than 94 percent over a 3 

year period.10 

Dairy 2007 study 

In 2007, the U.S. Department of Agriculture’s 

(USDA) National Animal Health Monitoring System 

conducted the Dairy 2007 study. The study was 

conducted in 17 of the Nation’s major dairy States*, 

representing 79.5 percent of U.S. dairy operations and 

82.5 percent of U.S. dairy cows. Operations were 

divided into 3 categories based on the number of dairy 

cows: small (fewer than 100 cows), medium (100 to 499 

cows), and large (500 or more cows). 

Objectives of the Dairy 2007 study included 

estimating the prevalence of specific food-safety 

pathogens and describing antimicrobial resistance 

patterns. No antimicrobial testing was performed for 

C. burnetii during the study; however, testing was done 

to estimate the herd-level prevalence of C. burnetii using 

bulk-tank milk samples from operations with 30 or more 

cows. 

Sample collection and testing 

To estimate the prevalence of C. burnetii on U.S. 

dairies, a single bulk-tank milk sample was collected 

from each of 528 participating operations from March 

through August 2007. On small operations, an average 

of 50 cows contributed milk to the bulk-tank samples. 

Samples taken from medium and large operations 

represented milk from an average of 166 and 958 cows, 

respectively. Samples were shipped overnight on ice to 

Antel BioSystems, Inc., which processed the samples 

and froze the resultant milk pellets. The resuspended 

milk pellets were sent to the Wisconsin Veterinary 

Diagnostic Laboratory where DNA was extracted and 

evaluated using polymerase chain reaction (PCR) to 

detect C. burnetii.

 

Results 

The percentage of operations PCR-positive for 

C. burnetii increased as herd size increased, with 69.8 

percent of small operations and 98.8 percent of large 

operations testing positive (table 1). Overall, milk from 

bulk tanks on more than three of four operations (76.9 

percent) tested positive for C. burnetii. 

____________________ 

*

States/Regions: 

 West: California, Idaho, New Mexico, Texas, and Washington 

 East: Indiana, Iowa, Kentucky, Michigan, Minnesota, Missouri, 

New York, Ohio, Pennsylvania, Vermont, Virginia, and Wisconsin 

Technical Brief
United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture 

Table 1. Percentage of Operations in which Bulktank Milk Tested PCR-Positive for C. burnetii, by 

Herd Size 

Herd size 

(Number of Dairy Cows) Percent Operations 

Small (fewer than 100 head) 69.8 

Medium (100-499 head) 90.8 

Large (500 or more head) 98.8 

All Operations 76.9 

A higher percentage of operations in the West 

region (see region breakouts on previous page) had 

bulk-tank samples positive for C. burnetii compared with 

operations in the East region (90.1 and 75.7 percent, 

respectively). 

 Operations PCR-positive for C. burnetii showed 

significant differences in health outcomes after adjusting 

for herd size and regional differences compared with 

operations that tested negative (table 2). Positive 

operations had a significantly higher percentage of 

calves born dead (6.6 percent) and a higher percentage 

of abortions (4.2 percent) than operations that tested 

negative (4.4 and 3.2 percent, respectively). In addition, 

positive operations removed a significantly higher 

percentage of cows due to reproductive problems. 

Table 2. Operation-level Health Outcomes by 

C. burnetii Status

C. burnetii 

Status 

Positive 

Operations 

Negative 

Operations

Health Outcome1

 Percent Percent 

Calves born dead2 6.6 4.4 

Abortions3 4.2 3.2 

Cows removed 

for reproductive problems3 7.4 5.2 

1

Adjusted for herd size and region. 

2 As a percentage of calves born. 

3

As a percentage of milk cows. 

Summary 

 C. burnetii is more prevalent in U.S. dairy herds than 

previously thought, and there may be a relationship 

between C. burnetii infection, abortion, calves born 

dead, and cows removed for reproductive problems. 

More research needs to be conducted to determine the 

source of C. burnetii on dairy operations and to 

determine what management practices are likely to 

decrease transmission of the organism. C. burnetii was 

detected in raw bulk-tank milk, but pasteurization 

inactivates the organism and provides a level of safety to 

the public. 

References 

1. Woldehiwet Z. 2004. Q fever (coxiellosis): epidemiology and 

pathogenesis. Res. Vet. Sci.. 77:93-100. 

2. Rodolakis A, Berri M, Hechard C, Caudron C, Souriau A, Bodier CC, 

Blanchard B, Camuset P, Devillechaise P, Natorp JC, Vadet JP, 

Arricau-Bouvery N. 2007. Comparison of Coxiella burnetii shedding in 

milk of dairy bovine, caprine, and ovine herds. J. Dairy Sci. 90:5352-

60. 

3. Coetzer JAW, Tustin RC. 2004. Infectious Diseases of Livestock, 

2nd ed. Oxford University Press Southern Africa. Cape Town, South 

Africa. 565-68. 

4. Cerf O, Condron R. 2006. For Debate: Coxiella burnetii and milk 

pasteurization: an early application of the precautionary principle? 

Epidemiol. Infect 134:946-951 

5.http://www.cdc.gov/ncidod/dvrd/qfever/ - Accessed October 2010. 

6. Guatteo R, Beaudeau F, Joly A. Seegers H. 2007. Coxiella burnetii

shedding by dairy cows. Vet. Res. 38:849-60. 

7. Barlow J, Rauch B, Welcome F, Kim SG, Dubovi E, Schukken Y. 

2008. Association between Coxiella burnetii shedding in milk and 

subclinical mastitis in dairy cattle. Vet. Res. 39:23. 

8. Paiba GA, Green LE, Lloyd G, Patel D, Morgan KL. 1999. 

Prevalence of antibodies to Coxiella burnetii (Q fever) in bulk tank milk 

in England and Wales. Vet Rec 144:519-22 

9. McQuiston JH, Nargund VN, Miller JD, Priestley R, Shaw EI, 

Thompson HA. 2005. Prevalence of antibodies to Coxiella burnetii

among veterinary school dairy herds in the United States, 2003. Vector 

Borne Zoonotic Dis 5:90-1. 

10. Kim SG, Kim EH, Lafferty CJ, Dubovi E. 2005. Coxiella burnetii in 

bulk tank milk samples, United States. Emerg Infect Dis. 11:619-21. 

____________________ 

For more information, contact: 

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NRRC Building B, M.S. 2E7 

2150 Centre Avenue 

Fort Collins, CO 80526-8117 

970.494.7000 

E-mail: NAHMS@aphis.usda.gov 

http://nahms.aphis.usda.gov 

#N579.0311 

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