Infectious Microorganisms: Introduction, Classification and Laboratory Safety Level

Infectious microorganisms

 Introduction of Infectious microorganisms 

The hidden role of Infectious microorganisms, in May 1847 Jakob Kolletschka, a Viennese doctor, cut his finger while doing an autopsy on a woman who had died of puerperal fever in the hospital. A few days later Kolletschka died.
In the US, Sulkin and Pike reported that 34 of 1342 laboratory infections occurring between 1930 and 1950 were due to mouth pipetting. Ricketts and Dr.  Carlo Urbani died of rocky mountain fever and SARS respectively while doing research on finding the cause. Cholera lab workers often died of the disease, CDC’s annual data approximately 12,000 HCWs have become accidentally infected with the Hepatitis B virus. Common causes of death from laboratory-acquired infections worldwide (except the UK) 1969-89
Typhoid fever-256
Streptococcal infection-78
Occupationally acquired HIV CDC by 1992 
Lab technician-25
Health attendant-6
House keeper-6

The above data has  confirmed that some organisms are
more hazardous to handle and are more likely to infect.

More pathogens are also becoming resistant
to available antimicrobial agents, making the treatment of
infections caused by these resistant organisms more

Classification of Infectious microorganisms

Classification of Infectious microorganisms is mandatory to maintain discipline in the sector of health security of the community as well as health workers. There is a variety of classifications of Infectious microorganisms according to institutions like CDC (Centers for Disease Control and Prevention), EU (European Union), and WHO but the core matter is the same. Here we discuss with WHO (World Health Organization) classification.

WHO classifies infective microorganisms into four risk groups and they are risk group 1, risk group 2, risk group 3, and risk group  4. The WHO recommends that the health authorities of each country should make lists of the organisms and viruses in each Risk Group, relevant to their local circumstances so that appropriate precautions may be applied. No one list will suffice for all countries because circumstances will vary from one region to another. e.g., if an organism is widespread in a community, there is no point in taking elaborate laboratory precautions to protect laboratory staff. Again, there will be little need to protect the community if an infection is unlikely to spread because of the absence of vectors or as a result of good sanitation or other public health measures.

Risk Group 1 Infectious microorganisms

Organisms are of no or low individual and community risk. A microorganism that is unlikely to cause human or animal disease. e.g. Food spoilage bacteria, common Mould, Yeast, Bacillus species, non-diarrhogenic E.coli.

Risk Group 2 Infectious microorganisms

Organisms are of moderate individual risk, low community risk. A pathogen that can cause serious human or animal disease but is unlikely to be a serious hazard to laboratory workers, the community, livestock, or the environment. Effective preventive measures and treatment are available and the risk of spread in the community is limited. e.g. staphylococci, streptococci, enterobacteria (except Salmonella Typhi), clostridia, vibrios, adenoviruses, polioviruses, coxsackieviruses, hepatitis viruses, Toxoplasma, and Leishmania.

Risk Group 3 Infectious microorganisms

It is of high individual and low community risk. A pathogen that usually causes serious disease but doesn’t ordinarily spread from one individual to another. It can escape from the laboratory. Effective treatment and preventive measures are available. eg. Brucella, Mycobacterium tuberculosis, Salmonella Typhi, Francisella, Pasteurella pestis, many arboviruses, LCM (Lymphocytic choriomeningitis ) virus, rickettsiae, chlamydia, Coccidioides, Histoplasma, human immunodeficiency viruses (HIV), Blastomyces dermatitidis, Paracoccidioides brasiliensis, Penicillum marneffei.

Risk Group 4 Infectious microorganisms 

The agents in this group offer high individual and community risk). A pathogen that usually causes serious disease and that can be readily transmitted from one individual to another, directly or indirectly. Effective treatment and preventive measures are not usually available. e .g. Marburg, Ebola, Lyssa, CFD (Creutzfeldt-Jakob disease), Equine encephalitis viruses, SARS (Severe Acute Respiratory Syndrome) virus, and certain arbovirus and they are haemorrhagic fever viruses.

Laboratory safety level for Infectious microorganisms

Risk Group 1: BioSafety Laboratory (BSL 1)-No Biosafety cabinet (BSC)

Risk Group 2: BioSafety Laboratory (BSL 2)- Biosafety cabinet 1

Risk Group 3: BioSafety Laboratory (BSL 3)-Biosafety cabinet 2

Risk Group 4: BioSafety Laboratory (BSL 4)-Biosafety cabinet 3

Further Readings

  1. Bailey & Scott’s Diagnostic Microbiology. Editors: Bettey A. Forbes, Daniel F. Sahm & Alice S. Weissfeld, 12th ed 2007, Publisher Elsevier.
  2. Clinical Microbiology Procedure Handbook Vol. I & II, Chief in editor H.D. Isenberg, Albert Einstein College of Medicine, New York, Publisher ASM (American Society for Microbiology), Washington DC.
  3. Colour Atlas and Textbook of Diagnostic Microbiology. Editors: Koneman E.W., Allen D.D., Dowell V.R. Jr, and Sommers H.M.
  4. Jawetz, Melnick and Adelberg’s Medical Microbiology. Editors: Geo. F. Brook, Janet S. Butel & Stephen A. Morse, 21st ed 1998, Publisher Appleton & Lance, Co Stamford Connecticut.
  5. Mackie and Mc Cartney Practical Medical Microbiology. Editors: J.G. Colle, A.G. Fraser, B.P. Marmion, A. Simmous, 4th ed, Publisher Churchill Living Stone, New York, Melborne, Sans Francisco 1996.
  6.  Manual of Clinical Microbiology. Editors: P.R. Murray, E. J. Baron, M. A. Pfaller, F. C. Tenover and R. H. Yolken, 7th ed 2005, Publisher ASM, USA
  7.  Textbook of Diagnostic Microbiology. Editors: Connie R. Mahon, Donald G. Lehman & George Manuselis, 3rd edition2007, Publisher Elsevier.
  8. Topley & Wilsons Principle of Bacteriology, Virology, and immunology Vol I, II, III, IV & V. Editors: M.T. Parker & L.H. Collier, 8th ed 1990, Publisher Edward Arnold publication, London.
  9. Medical Microbiology-The Practice of Medical Microbiology Vol-2-12th Edn. –Robert Cruickshank
  10. District Laboratory Practice in  Tropical Countries  –  Part-2-   Monica Cheesebrough-   2nd Edn Update


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