Early morning sputum is ideal for mycobacteriological exam for tuberculosis. Cough reflex is usually suppressed at night. Thus, the first early morning expectoration represents overnight secretions accumulated in the chest.
The 24 hour pooled secretion is poor because of frequent contamination with food particles, cigarette butts, etc. There is often an overgrowth of other bacteria as well, thus, making it unsuitable for AFB cultures.
The methods for obtaining sputum are:
If a patient denies any expectoration, you can attempt to induce it. You can do so by making the patient inhale heated 7% saline solution by a nebulizer. This irritates the respiratory tract and generates secretions that are suitable for studies.
Bronchoscopy is one method by which we can collect respiratory secretions for AFB. One should make sure that you have at least three negative sputum smears for AFB before attempting a bronchoscopy. You would like to avoid infection to the bronchoscopist. Bronchoscopy, in addition to permitting a lavage of the lesion for secretions, makes it possible for us to obtain a trans-bronchial biopsy of the lesion for histological and bacteriological evaluation of tissue.
Gastric lavage for collection of overnight respiratory secretions used to be commonly practiced during my internship days. Children and women tend to swallow sputum. During sleep, there may be a tendency to swallow sputum. The object of the gastric lavage is to collect the accumulated sputum from the stomach. To do it right, you should awaken the patient in the morning and so a gastric lavage before anyone in the room has breakfast delivered. Unfortunately, these rules are not routinely followed. If the patient has ambulated or has smelled his roommate's breakfast, he will develop a gastric contraction and empty the sputum into the small bowels.
Ziehl Neelsen Stain
Acid fast stain is not specific for M.TB. Many other organisms can have acid fast stain. However, if the clinical circumstance is appropriate, one can and should initiate therapy based on smears alone. Confirmation should be sought by cultures.
Culture confirmation should always be obtained to distinguish it from other mycobacteria. When necessary drug sensitivity can be performed only form culture.
There has been some radical changes in the medical profession over the past decade in regards to admission policies of patients with tuberculosis.
In the past, all patients with tuberculosis were admitted and kept in the hospital for protracted periods of time. Patients were admitted to Tuberculosis Sanitariums for care. They were not kept in general hospitals. Anyone with tuberculosis, or those suspected of having tuberculosis, were immediately hospitalized.
Things have since changed. We no longer routinely admit patients with tuberculosis. If a patient with tuberculosis requires admission, they are admitted to general hospitals. Most Tuberculosis Sanitariums have been closed.
Until recently, we never had any good therapy for tuberculosis. We relied totally on healthy food, fresh air and rest as forms of therapy. The major concern was infectivity of an active case. For this reason, patients were isolated. Major improvements in therapy have sine occurred. Tuberculosis is now curable with proper medications. Infectivity can be dramatically reduced by therapy. The reasons for routine admissions are now gone.
I admit a patient with tuberculosis if he is very ill, toxic or has major hemoptysis. There is no need to admit a patient just because he had been diagnosed as having tuberculosis.
This patient is a school teacher and has small children at home. Children are highly susceptible to tuberculous infection. Thus, my reasoning for admission. I can be challenged on this. The Madras Study (the place where I come from) will refute my reasoning. We will deal with this later.
This query is made to bring out the concept that most new cases of tuberculosis we see are due to reactivation of dormant organisms. Humans can deal with the first exposure to M.TB successfully and do not develop disease in general. When the patient's immunity decreases, due to some reason, the organisms reactivate.
Skin Test Results
PPD diluted should first be used in a person known to have been positive in the past. You should first have a reason why you want it repeated.
PPD higher strength is used if the intermediate strength is negative, you think the patient may be anergic and you strongly suspect the patient of having tuberculosis. Nowadays, we do anergy battery to judge whether the patient is anergic. I rarely find it necessary to use a higher strength PPD. PPD intermediate strength is the standard method.
Infection versus Disease
A positive PPD implies that the patient was infected in the past with M.TB. All patients with positive skin tests are considered to have been infected with M.TB.
Demonstration of tubercle bacilli from the patient is a marker for disease. You can be infected, but not have disease. When one develops disease, they will be ill with symptoms and you should be able to recover organisms from the lesion. This concept is going to be important when we consider prophylaxis.
Positive Skin Test: Infection
Demonstrable M.TB Organisms: Disease
How Infective is Tuberculosis
Suppose you have 100 children in a classroom and the teacher has active pulmonary tuberculosis. Initially, all of the children had negative skin tests. If you were to retest all the students after three months, approximately 25% would possess a positive skin test. Thus, approximately 25% of patients exposed to organisms would get infected.
Tuberculosis is of low contagion. You need protracted close contact to be infected. Tubercle bacillus multiplies slowly, hence of low infectivity.
Only a minority of those infected will go on to develop disease. Infection would be brought to control by our immune system in the remaining students. A positive skin test would be the only evidence for infection.
Mode of Spread
You should be aware of the concept of droplet nucleus and airborne mode of spread.
Infected patients excrete organisms in their sputum. When they cough or sneeze, they aerosolize the organisms into droplets. Larger droplets settle down. Smaller sized particles float in the air in the form of droplet nuclei. Whoever is in the room can inhale these droplet nuclei. Particles between two and five microns settle in the alveoli and respiratory bronchioles. This is how a patient gets infected. You cannot spread tuberculosis by clothing, gowns, utensils or other objects.
Infection does not necessarily follow exposure. Only a small percentage of people exposed develop infection.
Infection versus Disease
She has tuberculosis infection but not disease.
Infection: Positive skin test, no symptoms, no organism seen in sputum.
Disease: Positive skin test, has symptoms, demonstrable organisms seen in sputum.
Discuss the natural history of primary infection. Explain primary complex.
This phenomenon is due to gravity induced VQ relationship. Lobe bases have relatively more perfusion than ventilation. Thus, there is less oxygen in the alveoli. Since tuberculosis organisms are aerobic, they seem to thrive best in the apical segments of the lobes where there is relatively more ventilation compared to perfusion.
Did you know that Bats get TB primarily in the basal segments?
This may be the time to talk about current classifications of tuberculosis: Class 1, 2, 3, 4 and 5.
Control of contagiousness
Once the patient is on appropriate drugs, after 2wks he is non-infective.
Teaching the patient proper respiratory hygiene is very important. He should hold a kerchief or tissue in front on his face before coughing or sneezing. He should turn his head away from peopl respiratory passages. It is more important for the patient to wear a mask and cough using a kerchief held closely to their mouth. This will prevent aerosolization of sputum. The mask may prevent a large inoculum being sprayed on your face. Special mask fitted for individual use and offer better protection. Gowns are considered unnecessary.
Sunlight or ultraviolet light in the room are important in destroying organisms.
Ventilation from the room should not be recirculated. Hence, special rooms a