Comparison of Salivax™ HIV Saliva Test and Enzyme Immunoassay


basic information about oral fluids and their application as samples for HIV testing and summarises current understanding concerning the performance of HIV tests when used with oral fluids.


Oral Fluid Testing Advantages


The use of oral fluids for HIV testing offers several advantages over that of blood. Most importantly, sample collection is safer since occupational risk from needlesticks, disposal of needles and cuts from broken glass tubes are eliminated. In addition, the load of infectious virus in saliva is lower than that in blood.29–31


Disposal of wastes is an


important consideration in countries where incineration or autoclaving facilities are not available and where waste materials are buried or placed in open-refuse areas. With oral fluids, the disposal risk is minimised since a single collection device, usually made from an absorbent material, can be discarded with greater safety than a blood collection tube and needle. The collection of oral fluids may be simpler than that of venous blood, particularly from children, obese individuals and persons whose veins are not easily accessible. In some instances, adequate amounts of blood are difficult to obtain because of cultural/religious reasons and/or collapsed veins and several reports indicate that collection compliance is greater for oral samples than for blood. In addition, the use of oral fluids could help to reduce infection through the reuse of unsterilised needles. There may also be a cost saving when oral fluids are used as samples because collection requires minimal training of personnel. Furthermore, samples can be collected simultaneously from groups, while self-collection offers additional cost and time savings if large numbers of samples are to be collected. The cost of materials is lower when whole saliva (dribble) is used, but is comparable to the cost of blood- drawing materials if an oral collection device is required. Although blood collected by finger-, heel- or ear-lobe-prick may be the least costly of all methods, it may also be the most painful32


and involves disposal hazards. Disadvantages


and novel collection devices. Fourthly, large volumes of saliva for quality control panels will be much more difficult to obtain than blood and oral fluid conversion panels may be required for certain licensing agencies. Finally, the use of oral samples may raise concern about transmission of certain infectious agents, such as Mycobacterium tuberculosis and ethical/legal concern about the use (abuse) of easily collected samples for unsupervised HIV testing, e.g. home testing.


Components of Oral Fluid Saliva


The term saliva has been used loosely to describe fluids obtained from the oral cavity. Several types of fluids can be collected individually


EUROPEAN INFECTIOUS DISEASE


There are a few potential disadvantages related to the use of oral fluids for HIV testing. Firstly, it may be difficult to conduct unlinked anonymous studies for sentinel surveillance, which require that blood collected for a different purpose be used for HIV testing; currently, oral fluids are not collected for other testing purposes. However, this could change in the future since oral fluids are now being used to measure antibodies to other infectious agents such as measles and hepatitis viruses.12 Secondly, there is the potential for degradation of proteins, including immunoglobulins, by proteolytic activity if whole saliva is used without the addition of stabilisers. Thirdly, there is concern that some oral fluid samples may not possess sufficient quantities of immunoglobulin (total) and therefore may not be adequate to test for specific antibodies; however, this has been challenged owing to the development of sensitive assays33


from the oral cavity (salivary glands or the area at the tooth–gum margin) but most commonly a mixture of different fluids is collected. The term ‘pure saliva’ describes the fluid specifically derived from the submandibular, parotid, sublingual and labial salivary glands and must be collected by special methods. Pure saliva is composed mainly of a small number of immune and epithelial cells, small amounts of immunoglobulin (primarily of the secretory IgA isotype) and digestive enzymes such as amylase, zymogen granules and proteases. Some of these enzymes and perhaps more importantly, enzymes from bacteria that are normal flora, may degrade salivary proteins such as immunoglobulins, particularly if a secretory component of the immunoglobulin is not present.


The term ‘whole saliva’ is proposed for oral fluids collected directly (by dribbling or spitting). Whole saliva contains salivary gland secretions (pure saliva), products of the oral mucosa and gingival crevicular fluid (CF) – a fluid derived from the capillaries at the gingival–tooth margin.8


Crevicular Fluid


The terms ‘crevicular fluid’ (CF), ‘oral mucosal transudate’ (OMT), ‘gingival crevicular fluid’, ‘crevicular fluid saliva’ (CFS) and ‘gingival crevicular transudate’7,33


have all been used to describe those


oral fluids that are derived as an interstitial transudate, since immunoglobulin (mainly IgG) and other plasma components are passively transported from the capillary bed beneath the buccal and gingival mucosa to the oral cavity. The recent observation that the levels of albumin and immunoglobulin in serum and oral fluid do not correlate directly15


suggests that a mechanism other than


transudation could be responsible for the regulation of antibody levels in oral fluid. The composition of CF (similar to that of plasma but in quantities less than in serum) is most probably also altered due to the dilutional effect of saliva. CF is most easily obtained from the tooth–gum margin (gingival crevices and/or buccal mucosa) by collection with a special device or swab.


Mixtures


Regardless of the method used to collect oral fluids, saliva and CF will be collected together. The site of placement of collection devices in the mouth differs, however and therefore different devices may preferentially collect primarily one or the other fluid. As indicated below, one device is placed under the tongue, while another is placed along the tooth margin; a third device is chewed. Since IgG can be detected in fluids collected by all of these devices and in whole saliva collected by dribbling, each probably contains a mixture of saliva and CF. Individuals show variable levels of salivation when an object is placed in the mouth, and an increased production of saliva can act to dilute CF. Several investigators have suggested that the IgG concentration of oral fluids should be determined in order to assess the adequacy of sample collection, since the IgG concentration of some samples may be <0.1 mg/l, below the detection capabilities of some assays. However, the reported high sensitivities of some tests that use oral samples suggest that this may not be a significant problem.28,34,35


Immunoglobulin in Oral Fluid


The salivary glands have a local immunological system, including the production of secretory IgA, which constitutes about 87 % of the immunoglobulins in pure saliva. IgG is found in fluid from salivary


147


In this review, the term ‘oral fluid’ is used for fluids obtained from the oral cavity, without indication of their specific origin.


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