| Ch 16 | Page 12 / 16 | |
| Cancer emergencies |
Infections and cancer | |
Infections are one of the main problems in haematology: around 80% of patients with acute leukaemia, 75% of patients with lymphoma and 50% of those with myeloma will, at some stage, contract severe infection. In solid tissue oncology, infections are less frequent, with the exception of cases of intensive treatment or during the pre-palliative phase.
Many factors are implied in this increased infection risk:
Neutropenia is almost always induced by anti-cancer therapy, in particular chemotherapy. In order to obtain maximal efficiency, the dosage of modern chemotherapy (even in an adjuvant setting) is calculated in order to be just under the risk of febrile neutropenia, so that approximately 80 to 90% of the patients can be treated without severe neutropenia. Of course, since this is a statistical gamble, around 10 to 20% of patients will suffer, at least once after one course of chemotherapy, from febrile neutropenia or possibly an infectious episode.
The infectious risk is only increased when neutropenia falls under 1,000 per mm3, however it becomes very serious under 500 polymorphonuclears (PMN) per mm3 and almost constant when PMN counts are under 100 per mm3. The intensity of nadir (the lowest point on the curve), is far less important for infectious risk than the duration of this nadir. After a few days with a PMN level below 100 per mm3, the infectious risk is almost constant and requires preventive isolation measures.
Occasionally, patients suffer no severe neutropenia but an alteration of their phagocyte functions in relation to chemotherapy, resulting in the same effect.
Neutropenic patients do not express infections in the same manner as patients with normal leukocyte counts: they cannot produce pus or inflammation. For instance, they may have a severe lung infection, without purulent expectoration, but rather rapid respiratory insufficiency with pulmonary lesions which can very quickly become irreversible (necrosis without PMN reaction).
In a similar manner, they do not have pus in their urine but only bacteria. They do not harbour abscesses but necrosing lesions.
The most frequent sites of infection for these patients are: the throat, the lung, the urine, the skin and the perineal regions, and most infectious germs are those generally present in the patient’s body. Preventive measures are therefore most useful, in particular careful body washing.
Certain cancers, but to a greater extent, certain chemotherapies can lead to the severe depression of cellular immunity. Hence, since T lymphocytes and monocytes cannot be activated, numerous infectious factors will develop.
Among them, those expressed within the cell are the most fearsome.
For instance, bacterial infections with mycobacteria, listeria, nocardia, legionella, but also fungi infections with cryptoccoques, histoplasma, pneumocystis carinii, toxoplasmosis, or viral infections by cytomegalovirus or herpes simplex virus.
These disorders are mainly observed in haematological syndromes (myeloma, Waldenström’s disease). Hypogammaglobulinaemia or specific deficiencies in producing antibodies do not allow the humoral immune response and the adherence of germs through antibodies.
The difficulty in performing vaccinations during chemotherapy is also noteworthy.
Local mechanical factors induced by tumours may be responsible for the breach of natural anatomical barriers (for instance: local skin invasion, digestive tract invasion, respiratory airway invasion).
The obstruction of respiratory airways or digestive tracts also leads to a slowing of normal excreta flow (bronchial retention, intestinal occlusion).
The aggression of digestive or respiratory mucosae by chemotherapy (or radiotherapy) also promotes local super infection.
The presence of intravenous catheters, urinary catheters, tracheostomy, ureterostomy is an open door to germs. Prevention of infection during the fitting of intravenous catheters or devices requires rigorous surgical asepsis, high quality post-surgical care as well as surgical asepsis during the use of these devices, with, if possible, a delay between fitting and first use allowing sufficient healing time.
Only a few infections, frequently observed among cancer patients, will be revised here:
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