A4 FIS Abstracts

Pathology of Tropical Infections Professor Sebastian Lucas, London

The concept o f tropical infections is rather elastic.

Cer ta in tropical infect ions are only acquired outs ide U K .

These inc lude the fol lowing: Virus-: rabies, ye l low fever,

dengue , Ebola, Lassa , Marburg ; Bacteria:- Rickettsia spp

(non-Q), Yersinia pestis, Klebsiella rhinoscleromatis,

Pseudomonas pseudomallei; M y c o b a c t e r i a : - M. leprae,

M.uIcerans; F u n g i : - Histoplasma capsulatum,

Coccidioides immitis, Paracoccidioides brasiliensis,

Blastomyces dermatitidis, Penicillium marneffei;

Protozoa:- Plasmodium falciparum, Pl.vivax, Pl.malariae,

Pl.ovale, Trypanosoma brucei, T.cruzi, Leishmania spp.,

Isospora belli, Sarcocystis spp.; Nematodes; hookworms ,

ascarids, Strongyloides stercoralis, Trichuris, Onchocerca

volvulus, Wuchereria bancrofii, Loa loa, Driofilaria spp.;

Trematodes:- Schistosoma mansoni, S.japonucum,

S.haematobium, Paragonimus spp, Clonorchis spp.;

Cestodes:- cys t icercus (Taenia solium), Spirometra spp.

Other tropical infect ions are present in U K but are more

c o m m o n l y imported. T h e s e include: V i r u s : - hepati t is ,

A,B,C,D,E,F ,G, HTLV-1, HIV-2, (HIV-1); B a c t e r i a : -

Chlamydia trachomatis, Corynebacterium diphtheriae,

Vibrio cholerae, Salmonella spp, Shigella spp, Brucella

spp, Treponema pallidium, Borrelia (relapsing fever),

Calymmatobacterium granulomatis, Haemophilus ducreyi;

Mycobaeteria:- M.tuberculosis; F u n g i : - m y c e t o m a ,

c h r o m o m y c o s e s (eg p h a e o h y p h o m y c o t i c cyst); Protozoa:-

Entamoeba histolytica, Acanthamoeba spp.; Nematodes:-

Trichinella; Cestodes:- Echinococcus granulosus, Taenia

adult worms .

His topathological ly , the c o m m o n e s t encoun te red p rob lems

relate to tuberculosis , l e i shmanias i s , leprosy, amoebias i s ,

sch is tosomias i s , and mala r ia at autopsy. T hese will be

i l lustrated with reference to differential d iagnosis .

Blood Borne Virus Infections in Health Care Workers Dr Barry Evans, London

A renewed interest in blood borne viral infections followed publication in June 1997 of guidelines for the use of post exposure prophylaxis after occupational exposure to HIV in the UK(1). This interest has included surveillance of all occupational exposures to blood borne viruses, rates of transmission and mechanisms of exposure in health care settings.

There are two important public health aspects of blood borne virus infections and health care workers - (i) the risk of acquisition of hepatitis B, hepatitis C or HIV by health care workers from their patients and (ii) the risk of transmission from infected health care workers to their patients.

The prevalence of blood borne viral infections in populations can help in assessing the risks to health care workers. Within the UK we do not yet have good data on population prevalence of hepatitis C but it is likely to be less than 1% in the general population, but very much higher in groups such as injecting drug users. Hepatitis B surface antigen positive carriage is thought to be lower than that of hepatitis C with a general population carriage rate in the range 0.2% to 0.7%. As this is very ethnic group dependent it will vary considerably but will tend to be higher in certain urban areas. HIV seroprevalence rates are low in most centres outside London but in London, especially among certain risk groups, the rates are considerably higher.

Health care workers usually acquire blood borne viral infections in the occupational setting when they are performing exposure prone procedures or when they fail to follow, for whatever reason, predetermined guidelines. For instance, re-sheathing needles or lack of sharps boxes in the vicinity.

The risk of a health care worker acquiring hepatitis C from a percutaneous injury from an infected patient is of the order of 2- 3%. Risks from infected health care workers to patients are less clear but two instances have been described in the international literature.

Transmission of hepatitis B from patients to health care workers should be controlled by immunisation of health care workers. Risks of transmission from hepatitis B infected health care workers to patients still exist. Hepatitis B e antigen positive surgeons should not undertake exposure prone invasive procedures but surface antigen carriers (e antigen negative) are only excluded from undertaking such procedures if they have been shown to have been associated with transmission.

Acquisition of HIV by health care workers from a percutaneous injury from an infected patient is approximately 0.3%. Transmission risk of HIV from health care worker to a patient is low but problems exist with classifying high risk procedures and encouraging testing in look back exercises. Two instances of an HIV infected health care worker transmitting to patients have been described internationally (Florida dentist and Paris surgeon).

The best advice is still to avoid sharps injuries and this reduction of exposures is possible if universal precautions are adhered to. The invigorated surveillance system at the PHLS Communicable Disease Surveillance Centre for exposures to blood borne viruses is emphasising the necessity for primary prevention.

(1) Department of Health. Guidelines on Post-Exposure Prophylaxis for Health Care Workers Occupationally Exposed to HIV. UK Health Departments. June 1997.