Chap 27 Infectious and Communicable Diseases

Often, peripheral phagocytic cells encounter a pathogen first, but…

circulating B and T cells also are scouting for pathogens.

B cells’ role is to…

produce antibodies (humoral immunity). When B cell encounters foreign invader, antibody coats pathogen and facilitates phagocytosis.

T cells process antigens for…

B cells and include subpopulation of “killer cells.” 

• These cells play major role in cell-mediated immunity.

• Killer T -  directly attack infected cells

• Helper T - turn on cytotoxic “killer” cells

• Suppressor T -  turn off helper and killer T cells (control extreme responses)

Complement System:

proteins that coat bacteria to kill them directly and support neutrophils (blood) and macrophages (tissue) consumption of bacteria

Pathogen

—an organism that can cause disease in human host

• Classified by:

  • Shape (morphology)

  • Chemical composition

  • Growth requirements

  • Viability

• Rely on host to supply nutritional needs

  • Some pathogens (eg, certain bacteria) are equipped to survive outside host

  • Others (eg, certain viruses) can survive only in living cell

Factors that affect pathogen’s ability to cause disease

• Ability to invade and reproduce, and mode by which it does so

• Speed of reproduction, ability to produce toxin, and degree of tissue damage that results

• Pathogenicity and virulence

• Ability to induce or evade immune response in host

Mode of Transmission

Direct transmission results from physical contact between source and victim. 

• Examples include direct physical contact (handshake), oral contact, droplet spread, airborne spread, fecal contamination, and sexual contact. 

Indirect transmission results from the organism surviving on animate or inanimate objects for a time without a human host. 

• Examples include transmission by air, food, water, soil, or biologic matter.

External barriers - Flora

Nearly whole body surface is inhabited by normal microbial flora. 

• Flora enhances effectiveness of surface barrier by interfering with establishment of pathogenic agents.

External barriers - Skin

Prevents penetration of pathogens into internal environment of body

• Maintains acidic pH level that inhibits growth of pathogenic bacteria

External barriers - Gastrointestinal system

Normal bacteria in GI system compete with colonies of microorganisms that invade body for nutrients and space

• Normal bacteria help prevent growth of pathogenic organisms

External barriers - Upper respiratory tract

Sticky membranes of upper airway protect body against pathogens by trapping large particles; particles may then be swallowed or expelled by coughing or sneezing.

• Coarse nasal hairs and cilia also trap and filter foreign substances in inspired air, preventing pathogens from reaching lower respiratory tract.

External barriers - GU tract

Urination, combined with urine’s ability to kill bacteria help prevent infections in GU tract. 

• Antibacterial substances in prostatic fluid and vagina also help prevent infection.

Internal Barriers

Inflammatory response - second line of defense

• Inflammation—local reaction to cellular injury. 

  • Occurs in response to microbial infection and is activated when invasion of pathogen occurs. 

  • Works to prevent further incursion of pathogen by isolating, destroying, or neutralizing microorganism

• Inflammatory response usually is protective and beneficial, but sometimes it may initiate destruction of body’s own tissue.

• Inflammatory response may be divided into three separate stages. 

  • Cellular response to injury - inflammatory mediators, stimulation of inflammatory response

  • Vascular response to injury - hyperemia, chemotactic response migrates to affected tissue

  • Phagocytosis - leukocytes destroy pathogen, macrophages clear dead cells 

Latent Period

Begins when pathogen invades body 

Infection has occurred but infectious agent cannot be passed (“shed”) to someone else or cause clinically significant symptoms

Incubation Period

Interval between exposure to pathogen and first onset of symptoms

• Varies in length, ranging from a few hours to 15 years or longer

Communicability Period

Follows latent period

• Lasts as long as agent is present and can spread to other hosts

• Clinically significant symptoms from infection may manifest during this period

• Timing is variable, and may occur during the incubation and/or disease periods

Disease Period

Follows incubation period

• Varies in duration, depending on specific disease.

• May be free of symptoms or may be characterized by overt symptoms

• Symptoms can arise from invading organism or from body’s response to disease

Systemic Inflammatory Response Syndrome

Sepsis-3 criteria for SIRS defined as patient with suspected or confirmed source of infection and two or more of the following :

• Fever or hypothermia more than 38°C (100.4°F) or less than 36°C (96.8°F)

• Heart rate of more than 90 beats/min

• Respiratory rate of more than 20 breaths/min or arterial carbon dioxide pressure of less than 32 mm Hg

• Abnormal white blood cell count (leukocytosis, leukopenia, or bandemia)

Sepsis-3 SIRS criteria and other screening tools (SOFA and qSOFA) attempt to identify patients with increased risk for sepsis, septic shock, or severe outcome.

Sepsis and Septic Shock

qSOFA tool has been proposed to predict sepsis in prehospital setting. 

• Involves three assessments:

  • GCS13 or less

  • Systolic blood pressure 100 mm Hg or less

  • Respiratory rate 22 breaths/min or higher

• If two or more are present and infection is suspected, sepsis is predicted.

ETCO2 < 25 mmHg is great predictor of  mortality and severe sepsis

Sepsis Treatment

Adults: goal of MAP > 65 mmHg

• IV access

• 30 mL/kg fluid bolus (assess for signs of pulmonary edema)

• Vasopressors if hypotensive despite fluid resuscitation

Pediatrics:

• IV access

• 20 mL/kg fluig bolus, up to 60 mL/kg (assess for signs of pulmonary edema)

Human Immunodeficiency Virus (HIV)

Highest risk 

• High-risk sexual behavior (unprotected vaginal or anal sex)

• Sharing intravenous (IV) needles with an HIV-positive person

Less often

• Needlestick from HIV-contaminated needle or sharp object

• Infant born to or breastfed by an HIV-positive mother

Pathophysiology of Human Immunodeficiency Virus (HIV)

HIV infection results from one of two retroviruses

• HIV-1

• HIV-2

They convert to genetic ribonucleic acid (RNA) to DNA after entering host cell

Classifications and categories

Three categories based on CD4+ T-lymphocyte count or CD4+ T-lymphocyte percentage of total lymphocytes

For people 6 years or older:

• Category 1: Cell count of 500/mcL or higher (≥ 26%)

• Category 2: Cell count of 200 to 499/mcL (14% to 25%)

• Category 3: Cell count below 200/mcL (< 14%)

After viral transmission, the progression of HIV be divided into three stages:

Stage 1: Acute HIV infection

• Occurs 2 to 4 weeks after exposure

• Includes a flulike illness with fever, adenopathy, sore throat

Stage 2: Clinical latency

• No symptoms; virus reproducing slowly

• People taking HIV antiretroviral therapy diligently during this stage may have very low viral loads and are less likely to transmit the disease

Stage 3: AIDS

• Chills, fever, sweats, swollen lymph glands, weakness, weight loss

• Without treatment, patients who progress to AIDS typically survive about 3 years

Personal protection for HIV

Compliance with standard precautions is essential.

Risk to health care workers increases when:

• Exposure involves large amount of blood

• Exposure involves HIV-infected patient with terminal illness, possibly reflecting higher viral load in late course of AIDS

• Patients have high HIV count (viral load) in blood

Postexposure prophylaxis

• If exposure is confirmed or suspected:

  • Paramedic should immediately notify DICO (per protocol)

  • PEP should begin as soon as possible after exposure to HIV, and continue for 4 weeks

Hepatitis

Inflammation of the liver that can have many causes, including infection, drugs, and alcohol.

• Signs and symptoms

  • May not produce any symptoms

  • Typical—abrupt onset of flulike illness (fever, fatigue, nausea and vomiting)

  • Followed by abdominal pain, jaundice, dark urine, and clay-colored stools

• Patient treatment and protective measures

  • Treatment of patients with hepatitis in prehospital setting is mainly supportive.

  • Goal is to maintain circulatory status and prevent shock.

Hepatitis A Virus

Vaccine-preventable infection

• Incidence has declined in United States due to immunization

• Incidence much higher in developing countries

• May be acquired by Ingesting HAV-contaminated food or drink, or fecal–oral route

Adults not immunized should consider vaccination if they: 

• Live in a community with a high incidence of HAV infection

• Work or travel to countries with a high rate of HAV infection

• If male, have sex with other men

• Use illicit drugs

• Work with HAV-infected animals or with HAV in a research center

• Have chronic liver disease or clotting factor disorders

Hepatitis B Virus

Infectious HBV particles found in blood, secretions containing serum (eg, oozing, cutaneous lesions), and those derived from serum (eg, saliva, semen, vaginal secretions)

• Exposure occurs via:

  • Direct percutaneous inoculation (needle or transfusion of infected blood products) 

  • Indirect percutaneous (skin cuts or abrasions)

  • Absorption through mucosal surfaces 

  • Absorption of infective secretions 

  • Via environmental surfaces

Hepatitis B Virus - Pre and post exposure prophylaxis

Preexposure prophylaxis

• Health care workers who have developed antibodies to virus after immunization are at almost no risk of acquiring disease.

• HBV vaccination schedule generally requires three IM doses over 6 months.

Postexposure prophylaxis

• Exposure to HBV requires immediate evaluation. 

• Paramedic should report possible exposure to supervisory personnel and follow PEP guidelines established by medical direction and agency protocol.

• Those with known exposure and no or insufficient anti-HBs receive HBV vaccine and hepatitis B immune globulin.

Hepatitis C Virus

Bloodborne virus that causes a disease similar to that caused by HBV

• HCV infection most often results from injection-drug use, needlestick injuries, and inadequate infection control in health care settings.

• Much less frequently, it is acquired through sexual contact (especially men having sex with men), from unregulated tattoos, and in infants born to HCV-positive mothers.

No vaccine is available for HCV. Antiviral and immunologic treatments for HCV are more than 90% effective in controlling virus.

COVID-19

infectious disease caused by SARS-CoV-2 virus. 

• Virus spread primarily though aerosols and small airborne droplets that enter eyes, nose, or mouth. 

  • Also spread by hands that have contacted virus and subsequently touch eyes, nose, or mouth. 

  • Virus can spread by infected persons, regardless of whether they have symptoms. 

• Incubation period depends on viral variant; typically 5 to 6 days, up to 14 days. 

COVID-19 Signs and Symptoms

In some patients, disease is asymptomatic, detected only from testing. In others, disease progresses quickly to death.

Symptoms

• Upper respiratory infection: fever, sore throat, malaise, and cough

• Abdominal pain, vomiting, and loose stools

• Loss of the sense of smell (anosmia) or taste (ageusia) common in early strains

• Skin lesions (rash, discoloration of fingers and toes, or urticaria)

• Complications: ARDS, sepsis, DIC, liver and kidney injury, and pulmonary embolism

Some patients who recover from initial illness continue to experience symptoms (long COVID).

Tuberculosis - Risk factors 

Close contact with a person with infectious TB

• Immigration from an area with a high prevalence of TB

• Infants, children, or adolescents exposed to adults at risk for latent TB or TB 

• Living or working in high-risk environments (correctional facilities, homeless shelters, hospitals, and nursing homes)

• Health care workers who care for patients at risk for TB

Tuberculosis - Pathophysiology

TB is a chronic pulmonary disease acquired through inhalation of dried-droplet nucleus containing tubercle bacilli.

Affected organ systems

• Cardiovascular

  • Pericardial effusions

  • Lymphadenopathy (cervical lymph nodes are usually involved)

• Skeletal

  • Intervertebral disk deterioration

  • Chronic arthritis of one joint

• CNS

  • Subacute meningitis

  • Brain granulomas

• Systemic TB (extensive dissemination by the bloodstream of tubercle bacilli)

Tuberculosis - Testing

Signs and symptoms of initial TB infection may be minimal. 

• Early infection can be detected using:

  • Mantoux tuberculin skin test 

  • TB blood test

Tuberculosis - Signs and Symptoms

• fever

• weight loss

• night sweats 

• fatigue

• hemoptysis

Tuberculosis - Treatment

If effective treatment is begun without delay, TB is usually curable.

With latent TB, most patients are started on a drug regimen that may include: 

• 3 months of once-weekly isoniazid plus rifapentine

• 4 months of daily rifampin

• 3 months of daily rifampin plus isoniazid, pyrazinamide, and ethambutol

Active TB treatment can take 4, 6, or 9 months depending on the regimen. 

• Medications include moxifloxacin, rifapentine, isoniazid, rifampin, pyrazinamide, and ethambutol.

Patients infected with MDR-TB require treatment for up to 2 years.

Paramedics who have had a significant exposure should have a skin test immediately after exposure and again in 8 to 12 weeks.