L18 Acute Respiratory Tract Infections

The common cold is a self [blank_start]limiting[blank_end] illness (2 days - 2 weeks), characterised by nasal [blank_start]discharge[blank_end] and a sore [blank_start]throat[blank_end]. It is caused by [blank_start]viruses[blank_end], predominantly rhinoviruses. No treatment is required, but [blank_start]symptomatic[blank_end] relief is available. Complications in the elderly, young, and immunocompromised could be [blank_start]pneumonia and asthma attacks[blank_end].

A sore throat may be pharyngitis/tonsillitis. This can be viral or bacterial. 1. Viral: 80-90% of cases attribute to [blank_start]adenoviruses[blank_end]. A mild, self-limiting infection presenting with a [blank_start]sore[blank_end] throat, and [blank_start]slight[blank_end] fever. No treatment required except for [blank_start]symptom[blank_end] relief. 2. Bacterial: A more [blank_start]severe[blank_end] infection. The most common cause of bacterial throat infection is Group A [blank_start]Streptococcus pyogenes[blank_end] (GAS). Presents with a sore throat, [blank_start]fever[blank_end], and aching, swollen [blank_start]lymph[blank_end] nodes. Diagnosis is by throat [blank_start]culture[blank_end] and treatment is [blank_start]antibiotics[blank_end]. Common complications: abscess and [blank_start]rheumatic[blank_end] fever.

Diphtheria is a serious throat infection caused by [blank_start]Corynebacterium diphtheriae[blank_end]. It presents with a sore throat, headache, greatly [blank_start]enlarged[blank_end] cervical lymph nodes, low grade [blank_start]fever[blank_end], and [blank_start]grey[blank_end] mucus on tonsils. There is a gradual onset over [blank_start]2-5[blank_end] days, and it is transmissible for up to [blank_start]4[blank_end] weeks. It is [blank_start]toxin[blank_end] producing which causes heart & kidney [blank_start]failure[blank_end]. Prompt treatment with diphtheria [blank_start]anti-toxin[blank_end] is required & [blank_start]antibiotics[blank_end] are given even before confirmation by culture. 1 in [blank_start]10[blank_end] will still die from it. The last case in NZ was in 1998. There has been a vaccine available since 1926, which has been on the NZ immunisation schedule since 1941. It is a [blank_start]toxoid[blank_end] vaccine given as an intramuscular injection, between 87-98% effective in generating anti-toxin [blank_start]IgG[blank_end], though it declines with time, and boosters necessary & recommended at [blank_start]45 and 65[blank_end]. The vaccine is [blank_start]funded[blank_end] but not the administration. [blank_start]Pregnant[blank_end] women are funded.

Whooping cough, also known as [blank_start]pertussis[blank_end], is caused by a highly infectious (via [blank_start]droplets[blank_end]), and [blank_start]toxin[blank_end] producing bacteria, the gram negative bacilli Bordetella pertussis. It causes airway [blank_start]inflammation & oedema[blank_end], and airway [blank_start]cell[blank_end] death. The most at risk are [blank_start]infants[blank_end] too young to be immunised; Complications – pneumonia, convulsions, brain damage, death. 1 in 6 infants will [blank_start]die[blank_end] or have [blank_start]brain or lung[blank_end] damage. For adults and children, [blank_start]12-37[blank_end]% of persistent coughs are pertussis. There are [blank_start]2-5[blank_end] yearly epidemics. The highest rates are in Pacific and Māori infants, with [blank_start]51[blank_end]% hospitalized. There is a 4-fold increased risk of hospitalizations for children living in in [blank_start]deprived[blank_end] conditions.

Stages of Whooping Cough: After a [blank_start]7-10[blank_end] day incubation - • Stage 1 - ([blank_start]1[blank_end] week) malaise, low grade [blank_start]fever[blank_end], sneezing, runny [blank_start]nose[blank_end], dry [blank_start]cough[blank_end]. The [blank_start]most[blank_end] infectious stage. Antibiotic treatment at this stage can [blank_start]decrease[blank_end] severity of stage 2. Contacts should also be [blank_start]treated[blank_end]. • Stage 2 - ([blank_start]4[blank_end] weeks) short burst of extreme paroxysmal coughing (accumulation of [blank_start]mucus[blank_end]), vomiting, feeling of [blank_start]choking[blank_end], “whooping” between coughing fits. Still infectious, and [blank_start]few[blank_end] symptoms between paroxysms. Treatment here will not effect the disease but reduces [blank_start]transmission[blank_end]. • Stage 3 - ([blank_start]6[blank_end] weeks - months) recovery, cough less often. Prevention: - Vaccine available since 1945, on NZ immunisation schedule since 1960, i.m. injection - Moved from a cell-based vaccine to an [blank_start]acellular[blank_end] pertussis vaccine in the 1990s – less [blank_start]reactogenic[blank_end] but less effective. Boosters are required & funded. - It is recommended, but not funded that contacts & carers of [blank_start]newborns[blank_end] get boosters.

Influenza is an acute, self-limiting infection of the respiratory tract, causing fever, malaise, a sore throat, [blank_start]dry[blank_end] cough, and [blank_start]headache[blank_end]. It is caused by [blank_start]orthomyxovirus[blank_end] which has an RNA genome and 2 major surface [blank_start]glycoproteins[blank_end]; [blank_start]Haemagglutinin[blank_end] (H) and [blank_start]neuraminidase[blank_end] (N). There are 3 types of influenza viruses - A, B and C: A - evolves [blank_start]quickly[blank_end], causes [blank_start]human[blank_end] epidemics & pandemics, [blank_start]severe[blank_end] disease, H/N subtypes B - no H/N [blank_start]subtypes[blank_end], evolves more [blank_start]slowly[blank_end] than A, causes disease in humans, usually [blank_start]less[blank_end] severe C - no H/N subtypes, no disease in [blank_start]humans[blank_end]

Individuals can get influenza many times during life because the virus is continuously mutating.

Antigenic [blank_start]drift[blank_end] of the influenza virus causes seasonal variants. It occurs to overcome the [blank_start]antibodies[blank_end] blocking the H glycoproteins ability to bind to [blank_start]cells[blank_end]. It is a [blank_start]mutation[blank_end] of the H epitopes so that the antibody [blank_start]cannot[blank_end] bind and the virus may bind to the cell instead. Antigenic [blank_start]shift[blank_end] of the influenza virus causes epidemic/pandemic variants. It occurs when two viral strains exchange [blank_start]RNA[blank_end] segments in a [blank_start]secondary[blank_end] host and a [blank_start]novel[blank_end] H is formed.

Treatment for influenza is typically [blank_start]symptomatic[blank_end] relief of fever and pain with [blank_start]OTC[blank_end] meds. We can also use: 1. [blank_start]M2 Ion Channel[blank_end] Inhibitors (Cyclic Amines or Adamantanes) - amantadine, rimantadine: Inhibit viral [blank_start]uncoating[blank_end], which is symptomatic relief. Does not stop viral [blank_start]shedding[blank_end]. Has systemic [blank_start]toxicities[blank_end] and is associated with rapid induction of [blank_start]resistant[blank_end] viruses. 2. [blank_start]Neuraminidase[blank_end] inhibitors eg oseltamivir (Tamiflu) & zanamivir (Relenza): [blank_start]Pharmacist only[blank_end] medicine in NZ. Symptomatic relief via [blank_start]decrease[blank_end] of viral shedding, which reduces the [blank_start]rate of complications[blank_end]. May stop protective [blank_start]immune[blank_end] response developing. Has toxicities (especially [blank_start]zanamivir[blank_end]), and will induce viral resistance (especially [blank_start]oseltamivir[blank_end]). There is [blank_start]weak[blank_end] evidence that it may reduce mortality, hospitalisation and duration of symptoms, compared with no treatment.

Seasonal influenza prevention: - [blank_start]Inactivated[blank_end] vaccines against 3 or 4 circulating strains available – the supplier varies from year to year - Usually an intramuscular vaccine, which is [blank_start]funded[blank_end], effectiveness is [blank_start]~50[blank_end]%? - Funded in pharmacy for over [blank_start]65[blank_end]’s Pandemic influenza prevention: - H1N1 pandemic strain – now included in [blank_start]seasonal[blank_end] vaccine - H5N1 vaccine – Focetria® (Novartis), etc - H7N9 – pre-pandemic vaccines have been made by reverse genetics, not publicly available but [blank_start]stockpiles[blank_end] exist