Under the Microscope: Fatal Hazardous Infactions and Poisonings

Many forensic situations involve drug abusers and persons with promiscuous sexual behaviour, where the statistical risk of HIV and hepatitis infection is markedly greater than in the general autopsy population. This poses a risk to pathologists, mortuary staff, police and laboratory staff who may deal with post-autopsy samples.

All autopsies should be carried out with total precautions against infective risks, so that it does not matter what case is handled. However, this is almost impossible to achieve in a busy coroner or medical examiner practice and does not solve the problem of possibly infected material being sent out to other laboratories. A more common regime is to carry out pre-autopsy testing for HIV and hepatitis, using blood from a femoral needle puncture. The result can often be returned within hours, when a decision may be made as how to handle the autopsy - or even whether to abandon it, if the risk-benefit aspect is high. More usually, a positive result will result in the autopsy being carried out with special care, additional protective clothing, visors, masks and metal gloves, with restriction of access to observers, choice of more senior technicians and warnings sent to laboratories liable to handle samples.

In this respect, hepatitis is more of a risk than HIV infection. However, so far, about 100 health-care workers have acquired HIV infection from definite occupational exposure and one pathologist is known to have become infected from autopsy work.  Also three morticians in the USA have possibly contracted occupation-related HIV positivity.

 

The time for which a corpse remains potentially contagious with HN is variable. Infectious virus has been recovered from liquid blood held at room temperature for 2 months and virus in high concentrations has been found to remain viable for 3 weeks found 51 per cent survival of virus in plasma and monocyte fractions from infected cadavers up to 21 hours post-mortem. Other series found survival in corpses from 18 hours to 11 days after death. Virus has been recovered from the spleen after 14 days post-mortem. Refrigeration seems to make little difference to viability. Cultured blood and effusions from refrigerated bodies and obtained viable virus up to 16 days post-mortem and concluded that there was no safe maximum time at which corpses ceased to be an infective risk. In industrialized countries, it has become standard to offer post-exposure prophylaxis after significant percutaneous exposure to blood or tissues of HTV patients.

Toxicology has a number of different aspects and, in such a huge subject, various specialists have different interests. The clinical toxicologist is most concerned with diagnosis and treatment of the living patient; the analytical toxicologist has the complex task of laboratory investigation; and the pathologist is concerned with evaluating poisons as a cause or a contribution to death. Though obviously linked, these various aspects are substantially different and few people can claim to be proficient in all three. As far as the pathologist is concerned, his main task is to exclude or con- firm other non-toxic factors in the death. He has then to collect suitable samples for analysis and, when the laboratory results are available, to interpret them in the light of his knowledge of the history, clinical features and autopsy appearances.

 

The pathologist inevitably needs the expertise of the laboratory analyst and the latter's knowledge of the therapeutic, toxic and fatal levels of the substances under consideration. Such data must, however, be evaluated in the knowledge of other pathological and physiological conditions present, so that it is the pathologist, rather than the laboratory toxicologist, who should provide the final opinion upon the proximate cause of death. This does not always happen and some laboratory report forms may be seen that unequivocally - and unwisely - state that a particular drug caused the death. Where, as so often happens, the toxic levels found at post-mortem are not in a potentially fatal or even toxic range, then the pathologist should seek the advice of a din- ical toxicologist to determine whether any of the symptoms or signs during life may assist in deciding on the cause of death. As so often happens in forensic problems, the investigation of a fatal poisoning must be a cooperative effort, especially between pathologist and laboratory analyst. Even in apparently obvious cases, such as a blood saturation of 50 per cent carboxyhaemoglobin, it is not for the analyst to declare a definite cause of death, as the victim may also have had a fractured skull - but equally, the pathologist has an obligation to provide the laboratory with the best possible samples in the best possible condition, as well as good information about the circumstances of the case.

 

Many persons, including some doctors, are under the firm misapprehension that, for most toxic substances, there are relatively constant quantities that will cause death. Not only the lay public, but lawyers, police, coroners and others assume that there is a more or less linear relationship between the amount of poison that enters the body, the resulting levels in blood and tissues and the degree of disability caused - the ultimate disability being death. In addition, it is often thought. that back-calculation from blood and tissue levels can arrive at a definite assessment of how much poison was originally administered. This aspect is of particular concern to coroners and similar officers, who have to decide on motive in potential suicides, where the magnitude of any overdose may assist in distinguishing between accident and self-administration.

The pathologist has his own difficulties in respect of 'the fatal dose', as quantitative results from the laboratory have to be matched against a knowledge of published blood and tissue levels' for that substance in relation to its potential toxicity. Though numerous tables of toxic levels have been published, there is considerable variation between the levels recorded. Reasons for this are explored later. It is obvious that there is no 'fatal dose' in the sense of a single threshold concentration above which a person dies and below which he survives. Instead, there is a range of levels, the upper and lower margins of which vary from one authority to another, which encompasses most deaths - but even here there are many exceptions, instances being recorded where survival occurs well above the upper limit and death occurs below the lower margin. In such cases, the task of the pathologist is to evaluate all other non-toxicological data to see if they can modify the circumstances sufficiently to allow an accept- able explanation for the death. It is sometimes difficult to explain these concepts of great biological variation to lawyers and police officers, who expect more definite decisions, and might even feel that the is being evasive or obstructive.

Over a large number of tests, it provides a toxic level at which half the animals will be expected to die. Though the indicative value in a general sense in comparing the toxicity of one substance against another, there is no way of knowing whether the human victim of poisoning lies at the upper or lower end of the classical bell-shaped curve that characterizes most biological responses. Far more useful is the cumulative record of actual laboratory results from toxicology centres that deal with human poisoning, which progressively build up a large database of blood and tissue levels, and correlate these with records of the clinical state, toxic effects and fatal outcome. Even here the variations are wide, as the many published tables testify, but at least general guidance can be obtained.

 

Acknowledgements:

www.politie.nl  Politiekorpschef  @Janny Knol©

www.aived.nl    AIVD – @Erik Akerboom ©

www.politie.nl WEB Politie - @Henk van Essen©

 https://www.police-nationale.interieur.gouv.fr/ @ Stephane Folcher ©

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