Tuberculosis (TB) is a life-threatening, bacterial illness caused by a strain of bacteria that destroys biological tissues. The bacterial species producing the infection is called Mycobacterium tuberculosis. Usually, the lungs are disrupted more than other organs, although M. tuberculosis also can affect the pleura (the membranes between the lungs and the inner wall of the chest), lymph nodes, bones and joints, the kidneys and various other body organs and tissues, including the layers surrounding the brain, causing a complication called TB meningitis.
Whether pregnant or not, a woman can suffer symptoms over the course of weeks to months after what doctors call the primary TB infection (the time that the organism infects your body). Alternatively, you may be asymptomatic during the initial period after infection. Either way, your immune system learns to suppress the infection, keeping the bacteria in check for a while but without eliminating the bacteria. This is called a latent infection. While you are in latency, there are no symptoms and the TB infection is unlikely to transmit to other people. However, the infection can become activated later on, in which case it is called secondary tuberculosis, non-primary tuberculosis, or reactivation tuberculosis. Typically, this happens about two years after the initial infection.
M. tuberculosis infects one out of three people around the world, although the infection is more common in certain regions and countries. In most cases, it is a latent infection, but it is active in many people. In fact, in 2016, TB became active in 10.4 million people, killing 1.7 million. Also in 2016, the rate of active TB was 2.9 cases for every 100,000 people in the United States. There was a total of more than 9,000 US cases, which was a slight decrease from the previous year. However, the US Centers for Disease Control and Prevention estimates that approximately 14 percent of the US population is infected with tuberculosis. TB occurs twice as often in men as in women, but millions of women are infected. In 2011, 216,500 women were estimated to have active TB.
The risk of TB infection is influenced by a variety of factors. There is a high risk among immigrants from regions of the world with a high prevalence of TB, for instance. Also, carrying human immunodeficiency virus (HIV) increases the risk of having an active TB infection, plus alcohol abuse, homelessness, uncontrolled diabetes, chronic kidney failure, and having a family member with TB all increase the risk. Additionally, immunosuppressive medication given after organ transplantation, or to combat certain autoimmune diseases, increases the risk. In North America, the TB rate is elevated in African American, Asian, Latino, Pacific Islander, and Native American populations.
In many cases, the history and physical examination can suggest to the physician that a patient could be infected with TB. This triggers further investigation. In health care workers and medical or nursing students and other high risk groups, routine screening is needed with a handful of tests, the same tests that your doctor will order for you, if you are at risk of carrying TB. In one of the tests, known as the tuberculin skin or Mendel-Mantoux test, a small amount of protein derived from M. tuberculosis is injected into the upper layer of the skin. If a hard red bump developes within 48 hours, this suggests that you have been exposed to the organism. However, if you have received what’s called the BCG vaccine to protect against TB, the skin test will also come out positive.
A blood test called “interferon-γ release assay” is useful for determining whether a person has been infected with TB, whether or not he or she has ever received the BCG vaccine. The interferon-γ release assay cannot distinguish between a latent and active infection, so if it comes out positive, or if your TB infection status is not known, the doctor will order chest radiography, in which the lungs are imaged with X-rays. Chest radiography is not dangerous for a fetus or embryo particularly if performed with a modern X-ray machine that keeps the X-ray beam extremely focused. If the chest radiography suggests tuberculosis, you will be asked to expectorate sputum samples. A respiratory therapist may help you expectorate the samples; otherwise, a procedure called bronchoscopy can be order to obtain sputum from inside. Once sputum samples are obtained, they are examined for organisms called acid-fast bacilli. Additionally, a test called polymerase chain reaction (PCR) is performed to amplify DNA whose sequences can then be checked to identify any organisms present. Finally, sputum samples are cultured in the laboratory in an attempt to grow M. tuberculosis. If the organism is present, this test will reveal its vulnerability to various anti-TB antibiotic medications. However, it takes weeks to grow M. tuberculosis in culture. Thus, medications are started based on the clinical setting and the results of the quicker tests. If TB infection is suspected in the urinary system, then the doctor will need urine samples for testing.
TB can lead to holes and distortions in the airways and to lung infections and infections of the pleura, all of which can be fatal. As for the baby, infants born to mothers with active TB can suffer from low birth weight and possibly be born with a TB infection themselves.
Whether the doctor decides to treat a latent TB infection depends on various factors, such as whether you are infected with HIV or whether your immune system is suppressed because of drug therapy such as for organ transplantation. Another factor is the magnitude of positive results on the tests for TB. When latent TB gets treated, the standard treatment is a medication called isoniazid; this is taken for 6 – 9 months. As an alternative in latent TB, patients can take isoniazide together with another drug called rifapentine for 12 weeks.
Active TB infection in the lungs requires combination therapy consisting of more than one anti-tuberculosis medication. This is because use of just one drug leads to the organism developing resistance, meaning that the drug no longer works for that person and the infection returns with a vengeance. The usual regimen consists of isoniazid and rifampin, plus pyrazinamide and ethambutol. The four drugs are taken for two months. If tests on the sputum cultures then reveal that the TB that you have is sensitive to isoniazid and rifampin, the pyrazinamide and ethambutol are stopped and the therapy continues with just isoniazid and rifampin for another four months. If the TB turns out to be resistant to isoniazid and rifampin, this means that additional drugs are needed, depending on results of tests of the organisms that you carry. All four of the standard drugs are recommended in pregnant women in many countries, but in the US pyrazinamide is avoided in pregnant women with TB, of the TB organism is sensitive to isoniazid and rifampin. In these cases, the initial therapy consists of just the other three medications and the full treatment is extended to nine months, instead of six.
When a woman has active TB in organs other than the lungs, the four-drug treatment is given and may be to nine months, depending on the organ. Treatment can be even longer in cases of TB meningitis, in which case another groups of drugs called corticosteroids may be added, including if you are pregnant. To make treatment safe for you, a great deal of monitoring is necessary when you are pregnant. Throughout your treatment, you need blood tests and urine tests to make sure that the treatment is not damaging your liver, kidneys, or other organs. If there are signs that any drug is causing damage, the drug treatment may need to be adjusted.
All of the anti-tuberculosis drugs that are considered safe during pregnancy are also considered safe during breast feeding. Certain drugs can be excreted into breast milk, but they are not thought to harm a nursing infant at the levels that get into breast milk.