To detect and diagnose a Bordetella pertussis infection
When you have persistent, sharp spasms or fits of coughing (paroxysms) that the doctor suspects is due to pertussis (whooping cough); when you have symptoms of a cold and have been exposed to someone with pertussis
A nasopharyngeal (NP) swab or a nasal aspirate; occasionally, a blood sample drawn from a vein in your arm
This is a group of tests that are performed to detect and diagnose a Bordetella pertussis infection. B. pertussis is a bacterium that targets the lungs, typically causing a three-stage respiratory infection that is known as pertussis or whooping cough. It is highly contagious and causes a prolonged infection that is passed from person to person through respiratory droplets and close contact.
The incubation period for pertussis varies from a few days to up to three weeks. The first stage of the disease, called the catarrhal stage, usually lasts about two weeks and symptoms may resemble a mild cold. It is followed by the paroxysmal stage, which may last for one or two weeks or persist for a couple of months and is characterized by severe bouts of coughing. Eventually, the frequency of the coughing starts to decrease and the infected person enters the convalescent stage, with coughing decreasing over the next several weeks. Pertussis infection, however, can sometimes lead to complications such as pneumonia, encephalitis, and seizures, and it can be deadly. Infants tend to be the most severely affected and may require hospitalization.
Pertussis infections used to be very common in the United States, affecting about two hundred thousand people in epidemics that would occur every few years. Since the introduction of a pertussis vaccine and widespread vaccination of infants, this number has drastically decreased to several thousand a year. However, since neither the vaccine - nor the pertussis infection - confers lifetime immunity, health professionals are still seeing periodic outbreaks of pertussis in young unvaccinated infants, in adolescents, and in adults.
Pertussis testing is used to diagnose these infections and to help minimize their spread to others. Several different types of tests are available to detect pertussis infection. Some of these include:
- Detection of pertussis genetic material (Polymerase Chain Reaction, PCR)
- Direct fluorescent antibody (DFA)
- Blood tests for pertussis antibodies, IgA, IgG, IgM
Pertussis can be challenging to diagnose at times because the symptoms that present during the catarrhal stage are frequently indistinguishable from those of a common cold or of another respiratory illness such as bronchitis, influenza, and, in children, Respiratory Syncytial Virus (RSV). In the paroxysmal stage, many adults and vaccinated patients who have pertussis will present with only persistent coughing. Suspicion of pertussis infection is increased in patients who have the classic “whoop,” in people who have cold symptoms and have been in close contact with someone who has been diagnosed with pertussis, and when there is a known pertussis outbreak in the community. A pertussis culture and/or PCR test will usually be ordered on these patients but should not be performed on close contacts that do not have symptoms.
How is the sample collected for testing?
Sample collection technique is critical in pertussis testing. For a culture and/or a test for genetic material, a nasopharyngeal (NP) swab or nasal aspirate is used. The nasopharyngeal swab is collected by having you tip your head back and then a Dacron swab (like a long Q-tip with a small head) is gently inserted into one of your nostrils until resistance is met. It is left in place for several seconds, then rotated several times to collect cells, and withdrawn. This is not painful, but it may tickle a bit, cause your eyes to tear, and provoke a coughing paroxysm. For a nasal aspirate, a syringe is used to push a small amount of sterile saline into your nose, and then gentle suction is applied to collect the resulting fluid. For antibody testing, a blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
Como o exame é usado?
Pertussis tests are used to detect and diagnose a Bordetella pertussis infection. Early diagnosis and treatment may lessen the severity of symptoms and help limit spread of the disease.
There are several tests that may be used when a pertussis infection is suspected:
- Culture – this test has been the “gold standard” for identifying pertussis and is used to diagnose a pertussis infection. The sample is put into nutrient media and the bacteria are grown and identified. Results are reported in one to two weeks.
- Polymerase Chain Reaction (PCR) – this test amplifies the genetic material of the bacteria in a sample and is available within a couple of days.
- Direct Fluorescent Antibody (DFA) – this test is not as widely used as it once was. It is less specific and sensitive than the pertussis culture and PCR.
- Antibodies, IgA, IgG, IgM – these blood tests measure the body’s immune response to a pertussis infection.
Other tests that may occasionally be ordered include:
- Toxin antibodies, IgA, IgG – these blood tests measure the body’s immune response to toxins released by B. pertussis.
- B. pertussis molecular sub-typing – this test may be ordered not to benefit an individual patient, but so that health professionals can better understand the strain and severity of the B. pertussis present in a community during an outbreak.
Typically a pertussis culture and PCR test will both be ordered, as early in the illness as possible. Cultures are less likely to grow the organism 2-3 weeks into the illness, and cultures will be affected by some antimicrobial agents if the patient has been treated.
Since the introduction of PCR testing, the use of direct fluorescent antibody testing has significantly decreased. When used, it should be ordered along with a pertussis culture to recover the organism in order to investigate potential outbreaks and perform antimicrobial susceptibility testing.
Pertussis antibody testing is not used frequently. Acute and convalescent samples, collected several weeks apart, are sometimes ordered on a person who has not sought treatment until late in their illness or on an adult who has had a cough for an extended period of time. They are ordered to help determine if the person has had a recent pertussis infection. Pertussis IgG antibodies will be present in anyone who has been vaccinated. Pertussis IgM and IgA antibodies will usually only be present a short time after vaccination or infection. These tests may sometimes be ordered to help evaluate and study the spread of pertussis in the community. Rarely, an antibody test may be performed to evaluate the adequacy of a person’s immune response to a pertussis vaccine.
Quando o exame é pedido?
Pertussis tests are ordered when your doctor suspects that you have a Bordetella pertussis infection. A pertussis culture and PCR are typically performed when you have symptoms suggestive of pertussis, and as early in the illness as possible.
PCR testing should not be used to diagnose outbreaks of the disease. False positive results may occur when PCR is used to screen people who may have been exposed but have no symptoms of disease.
Symptoms during the first stage of the infection, called the catarrhal stage, may include typical cold symptoms such as a runny nose, sneezing, mild cough and/or a low-grade fever. After about two weeks, the paroxysmal stage begins and may include symptoms such as:
- Frequent severe bouts of coughing sometimes followed by vomiting
- Several rapid coughs followed by a whooping sound as the person inhales; affected adults may cough but not whoop, and infants may have trouble breathing and may choke more than whoop
These symptoms may last for one or two weeks or persist for a couple of months. During the convalescent stage, the severity of symptoms lessens, with the frequency of coughing gradually decreasing over the next several weeks.
O que significa o resultado do exame?
A positive culture is diagnostic for a B. pertussis infection, but a negative culture does not rule it out. Culture results are dependent on proper specimen collection and transport, duration of symptoms when the sample is collected, and prior antimicrobial therapy administered before the culture is taken.
A positive PCR test means that it is likely that the patient has pertussis. However, the PCR test may also be positive with other members of the Bordetella family. A negative PCR test means that it is less likely that the person has pertussis but does not rule it out. If there are an insufficient number of organisms in the sample, then they may not be detected. Both culture and PCR tests are less likely to be positive as the illness progresses.
The direct fluorescent antibody test is not as sensitive or specific as other methods. If it is positive, then the person may have pertussis, but this should be confirmed with a culture. A negative direct fluorescent antibody test does not rule out pertussis.
The presence of IgG B. pertussis antibodies may be seen with a recent infection but also after vaccination. A rise in the quantity of IgG B. pertussis antibodies between the acute and convalescent samples and the presence of IgM and IgA antibodies are evidence of a recent pertussis infection.
Há mais alguma coisa que eu devo saber?
The pertussis vaccination is given to infants as a series of shots. Those children who have not completed the series of pertussis vaccinations are at a higher risk of becoming infected. Even some people who have been vaccinated may be infected by Bordetella pertussis, but they will tend to have a less severe illness.
International travelers should be aware that many less developed countries do not have widespread vaccination for pertussis. Infants who have not completed their series of vaccinations and people who have not had a booster vaccination in many years may be at an increased risk of contracting pertussis.
Pode ser realizada cultura de amostra de garganta em vez de nasofaringe do meu nariz?
O teste para coqueluche pode ser feito no consultório médico?
Não. Não existe um teste diagnóstico simples e rápido para coqueluche. É necessário equipamento especializado e normalmente é realizado em laboratórios. Nem todos os laboratórios realizam esse teste e as amostras podem ser enviadas para um laboratório de saúde pública.
Por que o médico notificou a infecção pertússica do meu filho?
Por que não se ouve muito sobre coqueluche?
O número de pessoas afetadas caiu desde que a vacinação generalizada foi instituída nos Estados Unidos da América. Os bebês são vacinados rotineiramente, reduzindo a população susceptível. Os surtos de coqueluche são esporádicos em vez de sazonais, como a influenza e o VSR e, podem ser subnotificados e subdiagnosticados, especialmente em adultos, que podem não procurar tratamento quando apresentam sintomas de resfriados ou tosse persistente.
Meu médico disse que tenho Bordetella parapertussis. Este é o mesmo que tosse comprida?
A B. parapertussis é uma bactéria que pode infectar humanos da mesma maneira que a B. pertussis, mas a infecção normalmente provoca uma doença respiratória mais amena. Métodos de cultura e o teste de PCR podem detectar e distinguir a B. parapertussis da B. pertussis, e ambas são normalmente testadas, uma vez que o quadro clínico é semelhante. Não há vacina para prevenir infecções por B. parapertussis.
Conditions: Lung diseases
Em outros sites da Internet
American Family Physician: Pertussis, A Disease Affecting All Ages
CDC Travelers’ Health Yellow Book: Pertussis
Minnesota Department of Health: Pertussis (Whooping Cough)
Mayoclinic.com: Whooping Cough