NASAL DISCHARGE: WHAT IS IT FOR, PROCEDURE, CULTURE - BIOLOGY - 2024

The nasal discharge is a type of sampling used to the cytological or microbiological analysis. The cytological examination looks for the presence of eosinophils, among other types of cells. These indicate the possible etiology of the symptoms that the patient presents.

On the other hand, the culture allows the identification of the usual microbiota, as well as colonizing microorganisms, such as yeast and Staphylococcus aureus. Therefore, culture of nasal swabs is the ideal test to detect asymptomatic nasal carriers of Staphylococcus aureus.

Nasal mucosa and nasopharynx scheme. Source: Pixabay.com/translated by Rage against

Every day it is more important to know the cases of S. aureus carriage in asymptomatic patients, both at the hospital level and in the community, since multiresistant strains have been found, being a real danger as a disseminating factor.

On the other hand, the microbiological analysis of the nasal exudate, as well as the pharyngeal exudate, is a requirement demanded in some countries for the selection process of the personnel who will enter companies that handle food.

This is a preventive measure, as S. aureus produces an enterotoxin that causes food poisoning. The nasal exudate sample is very easy to take, although it is somewhat uncomfortable for the patient.

What is it for?

Sampling of nasal exudate is used to carry out two types of studies. Firstly, nasal cytology with eosinophil count can be performed and secondly it is useful for microbiological analysis.

Nasal exfoliative cytology

Nasal exudate cytology is necessary in the case of patients suffering from certain types of respiratory conditions, allergies or rhinopathies, among others. The allergist is interested in knowing what type of cells are shed from the nasopharyngeal epithelium, as well as the eosinophil count.

The result of the examination can guide the origin of the rhinitis, whether it is allergic or infectious, or whether the rhinopathy is inflammatory or not. Likewise, it is possible to differentiate between an allergic bronchitis from an infectious bronchitis.

However, this study must be accompanied by other analyzes so that it can be of real utility, since the results obtained must be associated with other parameters of importance, such as complete hematology, IgE determination, or series of feces.

It should be noted that in babies under 3 months of age there may be nasal eosinophilia without associated pathology. However, after this age, the presence of eosinophilia in nasal mucus without symptoms may be indicative of a future appearance of an allergic process.

Nasal swab culture

The culture is used to detect nasal carriers of S. aureus. Although the execution of this study is justified only in specific cases, it is useful because a significant percentage of the population carries S. aureus asymptomatically.

This analysis is mainly important for those who want to work handling food. In them, it must be ruled out that they are not carriers of this microorganism.

It is also useful in people who have repeated infections by S. aureus, such as impetigo, abscesses or boils, among other affections that suggest that the patient may be a chronic carrier. Sometimes it is important to study the closest family members as well.

On the other hand, on some occasions a culture of nasal exudate can be performed on health personnel, especially when there are significant outbreaks of this bacterium in the hospital area and no other possible source has been determined. In all the cases mentioned it is necessary to carry out the culture.

Sampling

-Cytology

Sampling can be done in two ways: spontaneous exfoliation or forced exfoliation with a swab.

Spontaneous exfoliation

The patient is asked to blow his nose strongly on a microscope slide. Then, with a swab or loop, the sample is spread.

Forced exfoliation with swab

The swab is introduced until reaching the inferior turbinates. Once inside, the swab is dragged along the walls giving turns to drag the cells. Because sampling is somewhat uncomfortable, the procedure should not take more than 10-15 seconds. The sample is then spread on a slide and allowed to air dry.

-Culture

To take the sample, proceed as follows:

- The patient is asked to tilt his head back a little.

- A swab is inserted to a depth of approximately 1 cm.

- The swab is dragged along the walls of the nasal mucosa, turning until it touches the greatest amount of surface.

- A sample must be taken from both nostrils. If the patient is to undergo cytology and culture, two samples should be taken per nostril. One will be for spreading on a slide and the other for culturing.

For culture, a single swab can be used for both nostrils. However, there are laboratories that prefer to take them with different swabs and when sowing they divide the culture plates into two halves, labeling them as follows: right nostril and left nostril.

In the case of the cytological study, it is recommended to make two smears, one from the right nostril and the other from the left.

Process

-Microbiological study (culture)

Ideally, once the sample is taken, it should be processed for culture, however this is not possible in most cases.

The swab (s) are placed in a transport medium if they are not to be processed immediately. There they can remain at room temperature. Ideally, the swab should be seeded in less than 2 hours; however in the means of transport it can last up to 24 hours.

The sample should be seeded on blood agar and salty mannitol. Blood agar and salty mannitol ensure isolation of S. aureus.

-Cytological study

The smears made are stained with Wright or Giemsa and observed under a microscope.

In cytology, a great diversity of cellular elements can be observed, depending on the condition of the patient. Each of these elements will guide the doctor towards the possible pathology. Although it is not a strong test, it does help to make differential diagnoses.

Among the elements that we can find are:

- Squamous cells.

- Macrophages.

- Cylindrical ciliated cells.

- Crystals from Charcot Leyden.

- Goblet cells.

- Polymorphonuclear.

- Eosinophils.

- Lymphocytes.

- Plasma cells.

-Eosinophil count

Hansel staining, described below, can be used for this technique.

materials

- Eosin.

- Methylene blue.

- Distilled water.

- 95% ethanol.

Process

Once the smear is dry in the open air, it is stained:

- A few drops of eosin are placed on the smear until the entire preparation is covered for 1 minute.

- The same amount of distilled water is added on top of the eosin for 1 minute.

- The liquid is thrown away and washed with distilled water.

- Tilt the sheet and let a few drops of ethanol fall on the surface as a wash.

- Add a few drops of methylene blue to cover the entire smear for 1 minute.

- Add the same amount of water on top of the methylene blue and leave for 2 minutes.

- Discard the liquid and wash with distilled water.

- Finally a few drops of ethanol are added and it is dried in the open air.

In a total of 100 fields, the percentage of observed eosinophils is measured.

Source: Prepared by the author MSc. Marielsa gil

recommendations

- Before taking the sample, the patient should not have placed drops or nasal washes.

- To carry out the culture, the patient must not be receiving treatment with antibiotics.

- For the eosinophil count, the patient cannot be on antiallergic drugs.

- It must be taken into account that this test is very nonspecific and that it can give false negatives in allergic patients treated with steroids.

References

1. Protocol, collection and transport of samples for microbiology. Donostia Hospital. Available at: osakidetza.euskadi.eus
2. Fosch S, Yones C, Trossero M, Grosso O, Nepote A. Nasal carriage of Staphylococcus aureus in individuals from the community: epidemiological factors. Acta bioquím. clin. latinoam. 2012; 46 (1): 59-68. Available at: scielo.org.
3. Platzer L, Aranís C, Beltrán C, Fonseca X, García P. Bacterial nasal colonization in a healthy population of the city of Santiago de Chile: Is there a carriage of methicillin resistant Staphylococcus aureus in the community? Rev. Otorhinolaryngol. Cir. Head Neck, 2010; 70 (2): 109-116. Available at: scielo.org.
4. Díaz A, Bravo M, Ceruti E, Casar C. Value of the eosinophil count in nasal discharge in the differential diagnosis of obstructive bronchial symptoms in children. Rev. Chilena Pediatría. 1973; 44 (4): 341-343.
5. Vallejos G, Téllez R, González A, Mena J, Reynoso V. Implications of eosinophils in the nasal mucus of patients with a possible diagnosis of allergic rhinitis. AN ORL MEX, 2007; 52 (2): 58-62