INFECTION SPREAD, PART I: PREVENTION
| PREVENTING INFECTIONS IN YOUR PATIENTS AND YOURSELF —Gregory J. Moran, MD, Clinical Professor of Medicine,
Department of Emergency Medicine and Division of Infectious Diseases, David Geffen School of Medicine at the University
of California, Los Angeles
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| Case 1: boy, 11 yr of age, played at construction site and stepped on nail, which went through tennis shoe into his foot;
boy healthy, and tetanus immunization current; has small puncture wound at base of foot; x-rays negative
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| Foot puncture wounds: risk for cellulitis, 2% to 8%, and for osteomyelitis, 0.04% to 1.8%; if infected, usually Staphylococcus
aureus (most common cause of skin and soft tissue infections); if osteomyelitis, Pseudomonas aeruginosa;
risk factors for infection—foreign body, type of footwear, and immunocompromise; Pseudomonas not common cause
overall of skin infections but lives in warm moist places; management—close inspection; cleaning; rule out foreign
body; coring not shown to reduce infection; irrigation may force bacteria in deeper; good aftercare instructions (advise
patient to return if signs of infection develop); prophylactic antibiotics—not shown to reduce or prevent infection; may
select resistant organisms; many cases of osteomyelitis occur despite anti-Pseudomonas antibiotics; in retrospective
study of ≈900 wounds, 16 patients (<2%) developed osteomyelitis, some of whom had debridement and probing and received
antibiotics
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| Antibiotic prophylaxis: not necessary for most simple wounds; incidence of infection low; certain subsets of lacerations
higher risk, eg, bite wounds; bites on hand especially high risk; data show risk for infection of dog bites to hand reduced
≈50% by prophylaxis; speaker recommends antibiotics for bites on hand, puncture wounds, and wounds with crush
injury; data show antibiotics—help in open fractures, penetrating abdominal wounds, and high-risk bite wounds; not
necessary in simple lacerations and extremity gunshot wounds; inadequate data—for foot punctures, ear cartilage, intraoral
wounds, contaminated wounds, immunocompromised hosts, and exposed tendon, but speaker usually gives antibiotics;
not necessary to give prophylaxis for long time (3 days usually sufficient); type of antibiotics—for bites,
amoxicillin and potassium clavulanate (Augmentin) covers Pasteurella (animal bite), Eikenella (human bite), Staphylococcus
, Streptococcus, and anaerobes; for oral wounds, penicillin (for normal oral flora); for most wounds on skin, first-
generation cephalosporins (Staphylococcus and Streptococcus); for high-risk open fracture, aminoglycosides added to
kill gram-negative organisms
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| Methicillin-resistant Staphylococcus aureus (MRSA): responsible for majority of skin and soft tissue infections in
United States; in most recent data (2001-2002), sample cultures from ≈10,000 people show 32% colonized with methicillin-susceptible
S aureus (MSSA) and 0.8% with MRSA; MRSA probably spread by infected people (not asymptomatic
carriers); study of soldiers during basic training showed 3% colonized by MRSA, 28% with MSSA; infection developed in
>33% of MRSA-colonized soldiers and in only 3% of those with MSSA; for prophylaxis, not necessary to cover for
MRSA, unless patient has had MRSA infection or if MRSA suspected; clindamycin one option for prophylaxis
|
| Case 2: man, 19 yr of age, arrives in emergency department (ED) with multiple gunshot wounds to chest and abdomen;
has gang-related tattoos and needle tracks on arms; during resuscitation, physician stuck in hand with contaminated needle
|
| Occupational body fluid exposure: in survey of health care workers, >50% reported percutaneous exposure, with
25% in past year; >50% of emergency physicians had ≥1 blood exposure in past 2 yr; Johns Hopkins study (1992)—
24% of patients in their ED had hepatitis B, hepatitis C, or HIV (16%); ED physicians should know relative prevalence
of common infectious diseases in area of practice; most people stuck by contaminated needle do not become infected;
some viruses more highly transmissible than others; risk for transmission with percutaneous exposure—hepatitis B,
2% to 40% (overall 5%-6%); hepatitis C, 2%; HIV, 1 in 300; needlestick evaluation—determine source and assess risk
factors; test source for hepatitis B surface antigen (HBsAg), hepatitis C virus (HCV) antibody (HCVAb), and HIV; for
exposed person, determine tetanus and hepatitis B vaccine status, and check baseline for hepatitis B virus (HBV), HCV,
and HIV (to determine whether subsequent seroconversion due to exposure at work)
|
| Hepatitis B vaccine: necessary to check antibody titer after series (to ensure response present); over time, antibody levels
wane (but immunized person still protected); no case of symptomatic infection, even with no measurable antibody level;
≈5% have inadequate response (need immune globulin [IG] if exposed)
|
| Hepatitis B immune globulin (HBIG): antibodies against HBV pooled from donors; gives passive immunity to those
who did not respond to vaccine or not previously vaccinated; usual dose 0.06 mL/kg intramuscularly (IM); provides protective
levels for ≈2 mo
|
| HBV postexposure prophylaxis (PEP): if worker unvacci-nated—if source HBsAg-positive, give HBIG and start
vaccine series; if source negative, start vaccine series; vaccinated worker—if antibody response known, no treatment
needed; if known nonresponder, give 2 doses of HBIG and may initiate revaccination; if antibody response unknown,
check for it; if adequate, no treatment; if negative and exposure high risk, HBIG added to vaccine booster dose
|
| HIV postexposure prophylaxis: risk-benefit decision; weigh drug toxicity and cost against likelihood of becoming
infected; for highest-risk exposures, PEP recommended; for lower risk, give PEP if worker desires; worker should participate
in decision; PEP should be initiated promptly (decide later whether to continue); if source available, obtain rapid
HIV test and act accordingly; for highest-risk exposure, issues include how much blood person exposed to and how much
HIV in that blood; for more severe stick (eg, hollow needle, deep stick, bloody) from source with high viral load (VL),
give 3-drug PEP; if less severe stick and source asymptomatic with low or no VL, give 2-drug PEP; for splash—2-drug
PEP, unless large-volume splash from source with high VL; no documented case of HIV transmission through intact
skin, so PEP not recommended; for source with unknown HIV status—decide on case-by-case basis; perform rapid
testing of source if available; can start PEP and stop if source tests negative; if source unknown or cannot be tested, PEP
usually not recommended, but consider 2-drug PEP in high-risk setting; no method for testing needles or other objects for
HIV
|
| Regimens for HIV PEP: standard protocol includes zidovudine (AZT) and lamivudine (3TC) available as single pill
(Combivir); for highest-risk exposures, add third drug, eg, lopinavir/ritonavir (Kaletra) for 4 wk (highest-risk period for
seroconversion); consider other drugs, depending on source patient (involve infectious disease specialist)
|
| Case 3: woman, 19 yr of age, at “rave” party; drinking alcohol; took pill (suposedly 3,4-methylenedioxymethamphetamine
[ecstasy]); woke up next day with no recollection of what happened, but believes she was sexually assaulted
|
| Sexual assault: collect evidence for potential prosecution; prophylaxis—includes oral cefpodoxime for gonorrhea,
azithromycin, and metronidazole (for Trichomonas and bacterial vaginosis [most common infection in women after sexual
assault]); begin hepatitis B vaccine series; for high-risk exposure, may add HBIG; consider HIV
|
| HIV risk from sexual exposure: factors to consider—frequency of exposure; probability that source HIV-positive;
probability of transmission; also consider—toxicity of PEP drugs; cost (≈$1000 for 4-wk course); on cost basis, PEP
not justified for low-risk exposures
|
| Risk for HIV transmission: with transfusion of HIV-infected blood, 100%; mother to infant, ≈25% chance without
prophylaxis; needlestick, 1 in 300; single sexual exposure (HIV-positive man to HIV-negative woman), probability of
transmission 1 in 1000; reasonable to recommend PEP in high-risk exposure; variables—extent of trauma, presence of
break in mucosa, anal intercourse, oral contact; start PEP within 72 hr (not absolute cutoff)
|
| Case 4: girl, 19 yr of age, with fever and vomiting; fainted at home; febrile, hypotensive, and looks sick; “crashes” in ED;
intubated; develops petechial and purpuric rash
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| Meningococcal disease: contact with index case increases risk of becoming infected; close contacts (eg, household
members, day care contacts) at increased risk; only people with direct hands-on contact at risk; PEP—rifampin; ceftriaxone;
ciprofloxacin used most commonly (single oral dose); for children, ceftriaxone; rifampin requires 4 doses
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| Case 5: man bumps leg; leg becomes more painful; overnight, leg becomes swollen; patient presents looking sick, febrile,
and confused; legs very swollen, with bullae and blisters
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| Group A Streptococcus: “flesh-eating” bacteria; group A streptococcal pharyngitis highly contagious; no good data on
skin infections; contact with infected person increases risk (low but still above baseline); PEP recommended for contacts,
eg, family members
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| Case 6: man, 17 yr of age, presents with abscess; history reveals repaired ventricular septal defect (VSD)
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| Prophylaxis for endocarditis: recommended for those with previous endocarditis (at highest risk), with prosthetic
valves, and for complex cyanotics (eg, tetralogy of Fallot); most other congenital heart diseases moderate risk, including
rheumatic heart disease; prophylaxis not required in patient with repaired VSD; if performing procedure reasonably expected
to cause bacteremia, prophylaxis against Staphylococcus and Streptococcus recommended (eg, first-generation
cephalosporin); not recommended for Foley catheter insertion, intubation, and injection of local anesthetic for vaginal delivery;
follow American Heart Association guidelines
|
| Summary: evidence to support prophylaxis for needlesticks for HIV, meningococcus, and influenza; no evidence that giving
antibiotics to patient with cold or respiratory infection prevents pneumonia; in sexual exposure, no good evidence to
support prophylaxis against HIV and sexually transmitted diseases; handwashing most important method of preventing infection
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| INFECTIONS FROM PETS —Jeffrey Bender, DVM, Assistant Professor, Department of Veterinary Public Health, College
of Veterinary Medicine, University of Minnesota, Minneapolis
|
| Zoonoses: transmitted by dogs—dermatophytes (ringworm infections); roundworms and hookworms; Campylobacter
and other enteric pathogens; rabies; transmitted by cats—cat scratch disease, toxoplasmosis, Pasteurella infection
from bites, Salmonella, Campylobacter, enteric infections, ringworm, and rabies; from pocket pets (eg, guinea pigs,
hamsters, mice, rats)—Pasteurella, Salmonella, Campylobacter, Leptospira, lymphocytic choriomeningitis virus
(LCMV; especially in organ-transplant recipients), and Streptobacillus moniloformis (rat bite fever)
|
| Reptiles and salmonellosis: reptiles carry Salmonella with no clinical signs; estimated carriage rate 50% to 90%; accounts
for 3% to 9% of human Salmonella cases; risky behaviors—bathing reptiles or cleaning reptile housing in bathtub
or kitchen sink; allowing reptiles to wander house, including kitchen; Centers for Disease Control and Prevention
(CDC) recommendations on who should avoid contact with reptile—persons at increased risk for infection or serious
complications include pregnant women, children <5 yr of age, and immunocompromised persons; family expecting child
should remove pet reptile or amphibian before infant arrives; reptiles not appropriate pets in child care centers; other animals
(eg, hamsters, mice)—carry and transmit Salmonella; outbreaks of multidrug-resistant Salmonella associated
with veterinary clinics and animal humane societies
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| Cats and toxoplasmosis: coccidian parasite associated with cats; cats definitive host; cats shed oocysts infective to other
intermediate hosts, eg, humans; prevalence especially high in countries where consumption of undercooked meat common;
400 to 4000 cases of congenital toxoplasmosis annually in United States, with 750 deaths annually; 50% believed associated
with eating contaminated undercooked meat; leading cause of chorioretinitis in immunocompetent people; most feral
cats or outdoor domestic cats infected, usually in first year of life; potentially shed up to 20 million oocysts daily (only for
2-3 wk); oocysts viable in environment for prolonged period; sporulation occurs 1 to 5 days after excretion; exposure not
from petting cat but from contact with place cat defecates and oocysts mature; serologic examination of cats of limited
value, except that seropositive cat (shedding completed) poses less risk to humans than seronegative one; life cycle—cats
defecate in grassy soil, exposing animals that humans consume, especially if undercooked, or even vegetables if consumed
raw; precautions—avoid eating undercooked meat; use irradiated or frozen meat; thoroughly wash or peel vegetables;
clean all cooking surfaces and utensils after contact with raw meat or produce; wear gloves while gardening; good hand hygiene;
precautions for cats—keep cats inside; use commercial cat food; avoid feeding raw or undercooked meat to cats;
cat litter should be changed daily by someone not pregnant; if pregnant, gloves should be worn and hands thoroughly
washed afterward
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| Toxocariasis: Toxocara canis (dog roundworm) and Toxocara cati (cat roundworm); individual female produces
200,000 eggs/day; with intestinal burdens, daily environmental contamination significant; most puppies and kittens infected;
veterinarians routinely deworm puppies and kittens multiple times, especially when young; once defecated, eggs
need several weeks to mature and become infectious; transmission occurs from eating contaminated soil; risk factors—
pica and presence of puppies in household; human infection directly from dogs or cats unlikely; in southern climates,
maturation process occurs more quickly; larval migration to lungs, liver, and other organs more concerning; roundworm
from raccoons (Baylisascaris) migrates to brain in humans; ≈750 cases of ocular larval migrans annually in United
States
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| Hookworms: common in puppies and kittens; one of leading causes of traveler’s illnesses, especially in Caribbean and
tropics (from dogs defecating on beach); prevention—good personal hygiene; wearing shoes; eliminating parasites from
pets; supervising and limiting children’s access to potentially contaminated areas
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| Group A beta-hemolytic streptococci (GAS): occasional case reports of households with ongoing streptococcal
infections that disappeared after treating pet; study looking at children with acute pharyngitis went into households and
cultured pets; in 230 of these households, no evidence of GAS found; probably human-to-human transmission
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| Mycobacterium tuberculosis: case report of Yorkshire terrier with tuberculosis (TB); dog living with person with TB and
had close contact and direct exposure to aerosolized droplets; study of dogs with TB found that all had history of contact
with clinically ill humans
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| Delusional parasitosis: mistaken belief that one is infested with ectoparasites or infected with internal parasites
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| MRSA in animals: seen primarily in dogs and cats (but occurs in other animals); animals brought in for nonhealing
clinical illness; case report—MRSA cultured from nose of healthy dog whose owner also colonized with MRSA (working
in nursing home); nurse treated twice with antibiotics (mupirocin, oral doxycycline, and rifampin) after outbreak in
nursing home; with evidence of recolonization, family screened and home environment assessed; found 1-yr-old daughter
with psoriasis colonized in nose and skin, and family dog colonized; concluded that nurse likely recolonized from
contact with baby, dog, or unknown source; treatment of mother, baby, and dog eliminated MRSA; lessons—evidence
of human-to-animal transmission and recognition that pets may act as ongoing sources of infection; potential nosocomial
and public health implications; owners instructed to consult with health care provider, encouraged to practice good hand
hygiene, and given educational materials; importance of monitoring for multidrug-resistant pathogens; need for good
communication between personnel and for good hand hygiene
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Suggested Reading
Chalmers JA et al: Antimicrobial prophylaxis for endocarditis: emotion or science? Heart 93:753; author reply 753,
2007; Eaton L: Hand washing is more important than cleaner wards in controlling MRSA. BMJ 330:922, 2005; McCausland
JB et al: Nonoccupational postexposure HIV prevention: emergency physicians' current practices, attitudes,
and beliefs. Ann Emerg Med 42:651, 2003; Mikulich VJ et al: Abridged version of the updated US Public Health Service
guidelines for the management of occupational exposures to hepatitis B virus, hepatitis C virus, and human immunodeficiency
virus and recommendations for postexposure prophylaxis. Ann Emerg Med 39:321, 2002; Milstone AM et al:
Alerting pregnant women to the risk of reptile-associated salmonellosis. Obstet Gynecol 107:516, 2006; Moloughney
BW: Transmission and postexposure management of bloodborne virus infections in the health care setting: where are we
now? CMAJ 165:445, 2001; Moran GJ: Emergency department management of blood and body fluid exposures. Ann
Emerg Med 35:47, 2000; Morris AM: Coming clean with antibiotic prophylaxis for infective endocarditis. Arch Intern
Med 167:330, 2007; Morrison G: Zoonotic infections from pets. Understanding the risks and treatment. Postgrad Med
110:24, 2001; Purcell B et al: Effectiveness of antibiotics in preventing meningococcal disease after a case: systematic
review. BMJ 328:1339, 2004; Senanayake SN: Prevention of meningococcal disease. N Engl J Med 356:525; author
reply 525, 2007; Voss A: Preventing the spread of MRSA. BMJ 329:521, 2004
Educational Objectives
| The goal of this program is to prevent the spread of infections in the health care setting and from pets to humans. After hearing
and assimilating this program, the clinician will be better able to:
|
 | 1. Decide when to give antibiotic prophylaxis for wounds and bites.
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| 2. Advise patients, including health care workers, about the probability of transmission of HIV and hepatitis B after exposure
to body fluids or sexual exposure.
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| 3. Prescribe adequate postexposure prophylaxis for hepatitis B and HIV.
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| 4. Diagnose diseases caused by pets and other animals.
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| 5. Educate patients about prevention of diseases caused by animals.
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Faculty Disclosure
In adherence to ACCME Standards for Commercial Support, Audio-Digest requires all faculty members to disclose relevant
financial relationships within the past 12 months that might create any personal conflicts of interest. Any identified
conflicts were resolved to ensure that this educational activity promotes quality in health care and not a proprietary business
or commercial interest. For this program, the following has been disclosed: Dr. Moran has received research grants from
Pfizer, Johnson and Johnson, and Wyeth Pharmaceuticals, and is on the Speakers’ Bureaus of Pfizer, Cubist, and Schering-
Plough.
Acknowledgements
Dr. Moran was recorded at 20th Annual Advances in Emergency Medicine and Primary Care, held April 18-20, 2007, in
Las Vegas, NV, and sponsored by the Olive View-UCLA Department of Emergency Medicine and the American College
of Emergency Physicians, State Chapter of California, Inc. Dr. Bender was recorded at Emergency Infections in Clinical
Practice and Public Health, held November 2-3, 2006, in Minneapolis, MN, and sponsored by the University of Minnesota
Medical School, Division of Infectious Diseases, Departments of Medicine and Pediatrics, Center for Infectious Disease
Research and Policy, the Minnesota Department of Health, Division of Infectious Diseases, and Mayo Clinic College
of Medicine, School of CME. The Audio-Digest Foundation thanks the speakers and the sponsors for their cooperation in
the production of this program.
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