Wednesday 12 December 2012

SEXUAL OFFENCES - FORENSIC SAMPLING

It is the practice in the west that forensic samples are obtained using a kit provided by the local police force. They advice their forensic medical examiners to refrain from using standard medical swabs and polypots. Unfortunately in our part of the world these sampling is done using locally made swabs and containers.


Sexual Examination Kit with combs

Swabs

Swabs


Principles of forensic sampling
 
Avoid contamination
I mentioned earlier about ‘cross contamination’ and how to avoid it. The sampling should be done with gloved hands. It is recommended that gloves should be changed after sampling each body orifice and surface. These used gloves should be used as a separate production.  It is also advisable to wear protective over cloth and a face mask if the examiner feels that he /she would cough or sneeze. However this may not be practical in our set up.
Preparation
The doctor should have discussed the kind of samples he should obtain with the police officer before he starts collecting them. Therefore, it would save time if samples are pre-labelled.
Double swabbing
This technique involves swabbing with a moist swab first and then with a dry swab. The swab should be moistened with sterile water first and then roll over the area to be swabbed. Immediately after that a dry swab is rolled over on the same area. By this way the dry biological material gets loosened up and absorbed by the second dry swab. These two swabs can be labelled A and B to show the sequence of swabbing.
Rolling over the swab
The whole of the swab head should be rolled over the area to maximize the surface area.
Number of Swabs
Minimum of two swabs are used on each site, one wet and one dry or if the area is moist two dry swabs. If a stain remains even after two swabs being taken, the swabbing should be repeated until the stain is completely removed. 
Control for water and swab
The doctor should remember to take a sample of water (into a dry swab) and a dry swab as control samples.
Packaging and Labelling
These samples should be properly bagged, labelled, signed, sealed and handed over to the police. (Ideally ‘tamper-proof’ bags should be used.

The samples to be taken in different types of sexual assaults
Vaginal Intercourse
After sexual intercourse spermatozoa and/or seminal fluid can be deposited on the vulva or in the vagina. Spermatozoa can be identified in the vagina swabs taken from post-pubertal women up to about 7 days after vaginal intercourse.  Two or more days after vaginal intercourse spermatozoa are more likely to be found in the endocervical swabs than vaginal swabs. It is reported that spermatozoa were found up to 10 days after vaginal sexual intercourse in the endocervix.

The following samples should be taken even if the patient is menstruating or has douched/washed/showered after the incident.  The current recommendation in the UK is that these samples should be taken if the patient complains of vaginal sexual intercourse during preceding 7 days or anal intercourse during preceding 3 days.

a.       Cut the matted pubic hair or swab the stained pubic hair.

b.      Loose hair and other material on the pubic hair should be removed with a single use disposable forceps.

c.       Comb pubic hair with a comb over a paper sheet. The comb and the folded paper sheet should be taken as a production. Cut 10-20 pubic hair as control sample.

d.      Two swabs (A & B) from vulva and perineum. If the stain or skin is dry use the double swab technique.

e.      Two swabs (A & B) from the low vagina (3-5 cm into vagina or lower half or third of vagina). If the vagina is dry the first should be moistened with sterile water.

f.        Ideally an appropriately sized speculum should be inserted to lower half or third of vagina and take sampling from the vaginal wall and fornicies using two dry swabs, one at a time. The speculum should lubricated. If a speculum cannot be inserted two dry swabs, one at a time, should be passed further into the vagina than the previous swabs and sample the high vagina.

g.       If the vaginal intercourse has occurred 2 or more than 2 days prior to examination and a speculum can be passed. Two dry swabs, one at a time, should be inserted through the speculum and sample from the endocervix.

h.      Speculum should be taken as a production or it should be swabbed. 

Anal intercourse
Spermatozoa can be identified from anal/rectal swabs taken up to 3 days of anal intercourse even when defecation occurred. As in the case of vaginal samples they should be obtained even if the patient defecated, washed or showered.

a.       Cut or swab the perianal hair if appeared stained with secretions.

b.      Foreign material including hair removed with disposable single use forceps

c.       Two swabs should be taken from the perianal skin (3 cm radius from the anus), first wet and the second dry. (Perianal swab)

d.      Two swabs, first wet and the second dry, inserted through the anal orifice (2-3 cm) and sample the anal canal. (Anal canal)

e.      Ideally an appropriate sized proctoscope is passed 3 cm into the anal canal and swab the lower rectum and anal canal using two dry swabs, one at a time.  (Rectum). The proctoscope should be lubricated.

f.        If it is not possible to pass the proctoscope two dry swabs, one at a time, should be passed into the anus and sample the anal canal and lower rectum. (Rectum/anal canal)

g.       Proctoscope should be retained or it should be swabbed.

Oral sexual act

Oral sexual act may include oral contact with vulva/vagina (cunnilinngus), anus (anilingus) or penis (fellatio).

If there is allegation of anilingus or cunnilingus within preceding two days swabs should be taken from vulva, low vagina and perianal region if the patient has not washed during that time. It is reported that swabs from skin may give positive results up to two days (DNA from deposition of saliva.)

After fellatio spermatozoa can persist in the mouth for two days. The following samples should be obtained if allegation of oral penile contact during preceding two days.

a.       Two swabs from the whole of the mouth including tongue, floor, teeth, gum and cheeks. (mouth)

b.      ‘Sterile water mouth wash’ into a polypot. (put some sterile water into the alleged victim’s mouth, ask her/him to gurgle thoroughly and put into a polypot.) (mouth washing)

c.       Sample of sterile water used to obtain the mouth wash is taken as a control sample.(control mouth wash)

If the patient is the subject of fellatio the following swabs should be obtained.

a.       Two, first wet second dry, swabs from coronal sulcus (coronal sulcus)

b.      Two, first wet second dry, swabs from glans penis (penis-glans)

c.       Two, firs wet second dry, swabs from the shaft of penis (penis-shaft)

Other general forensic samples

Depending on the circumstances other forensic samples may be requested by the police both from the alleged victim and the suspect. They may include:

a.       Head hair (combed, cut and plucked)

b.      Any loose material from head hair should be collected before combing using a forceps

c.       Nail scrapings and clippings from both hands. Scrapping is done first using ‘tooth pricks’ or pointed dry swabs. Then nails are clipped, ideally with disposable nail clippers. In our facilities a clean sterilized pair of scissors can be used. All fingers of one hand are scrapped on to a single sheet of paper and the ‘prick’ and the paper is collected as a production. Likewise alls the fingers of one hand is clipped on to a single sheet of paper and the ‘clipper’ and the paper is collected as a production.

d.      Wet and dry swabbing of the stains on the skin, hands, fingers etc.

Suspect

In addition to the general forensic samples following samples may be obtained from the suspect.

1.       Pubic hair can be swabbed or matted hair can be cut

2.       Collection of loose hair and other material from the pubic hair

3.       Two, first wet second dry, swabs from coronal sulcus (coronal sulcus)

4.       Two, first wet second dry, swabs from glans penis (penis-glans)

5.       Two, firs wet second dry, swabs from the shaft of penis (penis-shaft)

6.       Undressing and collection of clothing should be done in the same way as in the case of alleged victim
(These lecture notes were prepared from two books
1.       The physical signs of child sexual abuse, an evidence-based review and guidance for best practice, March 2008, Royal College of Paediatrics and Child Health.
2.       Clinical Forensic Medicine, 3rd Edition, Ed. W.D.S. McLay, 2009, Cambridge.)
Priyanjith Perera
12/12/12
 

 

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