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U.S. Department of Health and Human Services


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List of Terms: Q

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Did You Know?

The temperature required for pasteurization of milk was increased to destroy Coxiella burnetii organisms that cause Q Fever. Pasteurizing milk at 145° F (63° C) for at least 30 minutes or at 161° F (72° C) for 15 seconds is sufficient to destroy Coxiella burnetii.
“Q” stands for “query” because of the many unanswered questions posed by the new disease at the time of its first description.


> Q Fever  (also known as Rickettsial Pneumonia or Balkan Grippe)
An acute, systemic disease caused by the bacterium Coxiella burnetii, which grows only inside eukaryotic host cells.

This microorganism is the key target for milk pasteurization in the United States. Inactivation of Coxiella burnetii will ensure that tuberculosis bacteria will not be viable in milk.

Sources: Many species of ticks in various parts of the world keep the infection alive in nature by spreading the rickettsiae (parasitic bacteria) from animal to animal. Humans and their domestic livestock are infected only accidentally.

Because the rickettsiae are found in cow and goat milk, the ingestion of dairy products may play a role in the infection of humans and livestock. Q fever seems to be in large part an infection associated with particular occupations, such as those in the meat and dairy industry.


Incubation: Typically sudden, but may be gradual.

Symptoms: Fever, chills, headache, muscle aches, loss of appetite, disorientation, and profuse sweating. Although Q fever is, on the whole, a mild disease, it can sometimes result in severe and protracted illness. The outlook for recovery is excellent; the mortality rate is believed to be less than 1%.

Duration: 2 to 4 weeks.


> Qualitative Analysis
The process of testing for a substance to determine what it is and what its components are. The results are reported in terms of the presence or absence of particular components, based on the size of the sample used in the analysis, the number of samples analyzed, and the testing method. An example of qualitative analysis would be testing for the presence of the bacterial pathogen Listeria monocytogenes in a specific food.


> Qualitative Risk Assessment
Risk assessment that’s based on qualitative data or giving a qualitative result. The results are often stated in an estimated range, such as "there is a moderate to high risk of a certain outcome occurring" (also see Risk Assessment).


> Quantitative Analysis
The process of testing for a substance to determine how much of it there is and the numerical value of each of its components. An example would be testing for the amount or concentration of a certain chemical or microorganism, such as E. coli, in a food. In microbiology, this process is known as "enumeration." The results for a chemical might be given in concentration units - e.g., - parts per million (PPM) micrograms per gram (of the food).


> Quantitative Risk Assessment
Risk assessment that uses modeling to determine the probability(s) of what can go wrong, how likely it is to happen, and how severe is the health impact. The results are stated in numerical terms, such as "there is a 42% probability that one illness may occur from eating a serving of X food with a certain health outcome" (also see Risk Assessment).