Short Communication: A Simple Method for Performing Worm-Egg Counts on Sodium Acetate Formaldehyde-Preserved Samples

The Kato Katz method is the most common way of performing worm-egg counts on human faecal samples, but it must be done in the field using freshly collected samples. This makes it difficult to use in remote, poorly accessible situations. This paper describes a simple method for egg counts on preserved samples collected in the field and sent to a central location for further processing. 1. Introduction Faecal worm-egg counts for baseline surveys and for on-going monitoring and evaluation are an essential part of deworming programs [1]. The Kato Katz method [2, 3] is the most common way of performing worm egg counts on human faecal samples, but it requires the examination of fresh faeces in the field. That makes it very difficult to use in areas such as the Central Pacific where it may mean deploying a team of microscopists, their equipment, and supplies to a remote island only accessible by an unreliable shipping service, or the remote areas of Papua New Guinea where access is by expensive air services that can be delayed for days, and even weeks, by adverse weather. Other problems with the Kato Katz method include the need to examine the preparation within 30 minutes to prevent overclearing and underestimation of hookworm eggs [1], the inability to keep samples or slides for reexamination for quality control, the risk of infection from the faeces sample, and last but not least, the safe disposal of the discarded materials, especially glass slides, on small isolated atolls and islands where the dealing with of any sort of rubbish is difficult. All of the above problems can be overcome by using Sodium acetate, acetic acid, formalin (SAF)-preserved samples [2] which remain stable for long periods even when stored at ambient temperature. The collection containers and preservative can be sent to the survey site ahead of time, the samples collected by local health workers and sent to a central laboratory for processing when transport is available. The problem is devising a method for egg counts on faecal samples that have already been diluted with preservative. One way to do this is to add a weighed amount of faeces to a known volume of preservative but that would require suitable balances to be available at the field collection sites. The newly introduced “FLOTAC” method [4] can also be used on preserved samples but requires specialised equipment. Other advantages of having SAF-preserved samples is that they can be used to conduct a more comprehensive parasitological survey because concentration methods can be used to detect “rare” eggs and permanent stains