Part III: Culture
specimen storage and transport

For successful culture of specimens the time between specimen collection and the culturing process should be kept to a minimum. Specimens should therefore be dispatched with the least possible delay. If sputum specimens can be kept refrigerated they could be sent to the laboratory once a week; extra-pulmonary specimens, however, should be submitted as soon as possible after collection.

If specimens have to be transported at ambient temperatures, chemical preservation may be used. Three methods provide reasonable results, viz:

• Mixing the fresh specimen with an equal  volume of 1% cetyl pyridinium chloride in 2% sodium chloride. Tubercle bacilli will survive for up to a week, while the growth of unwanted organisms will be restricted
• Mixing the fresh specimen with anhydrous sodium carbonate in the proportion of 50mg reagent to 2ml specimen
• If the delay before cultural examination is to be less than 24 hours the specimens may be mixed with an equal volume of 23% trisodium phosphate

However, none of the abovementioned preservation methods is optimal and speedy transportation is essential for good results.

Requirements and recommendations for the safe transport of pathological specimens are given in various national and international codes of practice and guidelines. In addition, the postal and transport authorities of most countries as well as the International Air Transport Association (IATA) have regulations about conveying such materials.

As a general rule, diagnostic specimens must be packaged to withstand leakage of contents, shocks, pressure changes and other conditions incident to ordinary handling practices. Pathological material intended for postal or air transport should be in approved, robust, leak-proof primary containers which are packed into secondary containers made of metal, wood or strong cardboard with enough absorbent material so that if they are damaged or leak the fluids will be absorbed. For sending material across international or state boundaries this container may have to be packed in the same way in an outer container and special administrative arrangements with the postal authorities and airlines may be necessary.

Sputum specimens comprise the majority of specimens submitted to tuberculosis culture laboratories and special transport boxes of metal or wood should be provided. They should be made to hold between 20 and 30 specimen containers packed vertically to avoid leaking. The lid should be securely fastened and the box should preferably contain a locking mechanism. During transport it must be kept as cool as possible and protected from sunlight.

Request forms should be located separately from specimen containers. With each transport box an accompanying list must be prepared which identifies the specimens and the patients from whom the specimens were collected. Before dispatch from the health centre the following must be verified:

• that the number of specimen containers in  the box corresponds to that on the accompanying list
• that the identification number on each specimen container corresponds to the identification number on the accompanying list
• that the accompanying list contains the  necessary data for each patient
• that the date of dispatch and the  particulars of the health centre are on the accompanying list

A model laboratory request form is presented in Annex 3.