Lecture 18 Clinical Microbiology

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Lecture 18Clinical Microbiology

• Aims
• To become aware of the basic tenets of infection
  control
• To understand the the nature of community
  acquired infections

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Infectious disease controlThe nature of outbreaks

• Epidemiology
• The study of how diseases occur and move through
  a community
• eg an investigation into the nature of an
  outbreak of salmonellosis in the Toowoomba region

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Infectious disease controlThe nature of outbreaks

• Aetiology
• The study and definition of the causative agent
  of a disease
• eg determination that the outbreak of an enteric
  disease in Toowoomba was due to Salmonella sp

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Infectious disease controlThe nature of outbreaks

• Epidemic
• of a disease (incidence higher than the normal
  background rate) in a specified time with a
  specified region
• eg. An outbreak of food poisoning due to
  Staphylococci in the Brisbane region

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Infectious disease controlThe nature of outbreaks

• Pandemic
• An outbreak of disease in a specified time
  (incidence greater than the normal background
  rate) involving continental or transcontinental
  occurrence
• eg outbreak of influenza virus spanning Europe,
  Asia and Nth America

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Infectious disease controlThe nature of outbreaks

• Endemic
• A disease that is always present in some members
  in a specified geographical location
• eg HBV is present always present in some members
  in Asia

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Infectious disease controlThe nature of outbreaks

• Prevention of infectious diseases may be applied
  at 3 levels
• Primary
• Secondary
• Tertiary

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Infectious disease control

• Primary control
• Refers to measures that are aimed at preventing
  exposure to infectious agents
• eg. Vaccination against influenza virus
• spraying insecticides to prevent malaria
• education program to prevent HIV, HBV/C

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Infectious disease control

• Secondary control
• measures directed at limiting the spread of an
  infectious agent
• eg vaccination in the face of an outbreak
• screening patients
• cohorting patients
• hygiene issues

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Infectious disease control

• Tertiary Control
• Tertiary control is directed at controlling the
  impact of outbreaks
• eg outbreak of meningitis due to N.meningitidis
  by providing prophylactic rifampicin to close
  contacts of index case

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Community acquired infections

• Defined as infections which are found to occur in
  the general community as distinct from infections
  occurring in institutions
• eg Pneumonia as a result of S.pneumoniae infection

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Community acquired infections

• Infections within the community often vary quite
  significantly to found in specialized
  environments such as hospitals
• predominant influence is the pool of infectious
  diseases (reservoir) and the mode that the
  microbes circulate (transmission)
• at any one time in a community such as ours about
  5 show some evidence of infection

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Community acquired infections

• Many infections arise from resident flora
  (endogenous)
• Often arise due to some transient episode eg
  spell of cold weather
• Such influences allow opportunistic pathogens to
  proliferate leading to overt disease (often
  secondary infections)

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Community acquired infections

• Broad spectrum antibiotics are often prescribed
  by clinicians because of educated guess rather
  absolute information about pathogen
• Can lead to problems if antibiotic spectrum does
  not cover target organism and another is required
• eg Penicillins used to treat mycoplasma-consequent
  ly requires erythromycin

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Community acquired infections

• Within community acquired infections most severe
  outbreaks are associated with efficient modes of
  transmission
• eg the low incidence of enteric infections is due
  to the quality of sanitation and potable water
• cw Flu A and the respiratory route (difficult to
  prevent- other than vaccination an herd immunity)

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Community acquired infections

• Patterns of health care delivery
• Use of antibiotics can have implications within
  the community and in hospitals
• eg Norfloxacin (ciprofloxacin) story and
  pseudomonas
• Common use of more advanced penicillins has lead
  to development of resistance in staphylococci in
  urban environments

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Community acquired infections

• Over generalisation?
• Healthcare practices (especially moves to
  community based nursing for chronic diseases)
• eg treating cancer patients, HIV etc at home may
  have ID implications not previously experienced

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Community acquired infections

• Changes in community attitudes
• reduced compliance in childhood vaccinations has
  reduced the level of herd immunity and
  consequently increasing the numbers of
  susceptible hosts

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Community acquired infections

• Status of patients
• As in hospitals the status of the patient has a
  significant influence on ID outcomes
• Opportunistic pathogens play a significant role
  as they tend to be part of the normal flora and
  less transient than true pathogens

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Community acquired infections

• What occurs in the community?
• The status of the patient has a significant
  influence (vaccinated? Young, elderly)
• if there is no underlying disease the spectrum is
  ID agents tend to be toward true pathogens
• Debilitated patients the spectrum widens to
  include opportunistic pathogens

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Community acquired infections

• The definition of pathogen within the community
  needs to be revisited
• Note carriage by healthy adults of the following
  ID agents has been recorded
• 10-20 S.pneunomiae
• 10-20 H.influenzae N.meningitidis
• 10-15 GBS in adult females

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Community acquired infections

• Carrier status
• In essence many of the previous patients are in
  act carriers
• That is they carry pathogens without overt signs
  of disease
• carrier may eventually succumb to the disease (eg
  HBV)
• In some cases less susceptible
• eg N. meningitidis

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Agents of neonatal meningitis

• E.coli cefotaxime/gentamicin
• H.influenzae cefotaxime
• GBS penicillin G

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Infant/adult meningitis

• N.meningitidis Cefotaxime
• S.aureus flucloxacillin
• Streptococcal sp penicillin G/amoxicillin

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Pneumonia

• Infantile
• H.influenzae cefotaxime
• S.pneumoniae penicillin G
• Adult
• S.pneumoniae penicillin G
• H.influenzae cefotaxime
• S.aureus flucloxacillin
• M.pneumoniae erythromycin
• Other