Influenza
Influenza is also called the flu. It is a viral infection caused by influenza viruses. The symptoms may be mild to severe and are usually accompanied by fever runny nose sore throat muscle aches headache coughing and tiredness. The symptoms start one to four days from exposure to the virus and last for approximately two to eight days. There may be diarrhea and vomiting especially in children. Influenza can advance to pneumonia due to the virus or a secondary bacterial infection. Acute respiratory distress syndrome meningitis encephalitis and exacerbation of existing health issues like asthma and cardiovascular disease are some of the complications.
Four types of influenza viruses are many types. Aquatic birds are the main source of influenza A virus which is also prevalent in other mammals including humans and pigs. Influenza B virus IBV and influenza C virus ICV infect humans and influenza D virus infects cattle and pigs. Influenza A virus and influenza B virus infect and seasonally epidemically affect humans and influenza C virus causes mild infection mostly in children. Influenza D virus infects humans but is not reported to be disease causing. In humans influenza viruses are spread mainly through respiratory droplets from coughing and sneezing. Aerosol and surface virus-contaminated transmission also occurs.
Hand washing and covering the mouth and nose when coughing and sneezing decrease transmission as does mask-wearing. Annual vaccination will protect against influenza. Influenza viruses and especially the influenza A virus change rapidly so flu vaccines are revised every year to align with which influenza viruses are present. Vaccines are against influenza A virus subtypes H1N1 and H3N2 and a single or two influenza B virus subtypes.
Influenza infection is diagnosed using laboratory tests like antibody or antigen tests and a polymerase chain reaction PCR to detect viral nucleic acid. The illness can be managed with supportive care and in serious illness with antiviral agents like oseltamivir. In otherwise healthy persons influenza is usually self-limited and seldom fatal, but it is potentially lethal in at-risk groups.
Risk of Influenza
Infection with Influenza A virus generates high annual morbidity and mortality throughout the world, especially for infants the elderly and immunocompromised persons. The virus primarily grows in the respiratory tract and is transmitted by respiratory secretions. Rising is the recent discovery of Asian H5N1 strains of avian influenza A previously known to infect only poultry and wild birds but has now infected cats humans pigs and other mammals usually with deadly consequences in an ongoing epidemic. An H5N1 human pandemic can be potentially devastating since most populations of humans carry very little antibody-mediated immunity against the H5 surface protein and the viral subtype is highly virulent.
If an H5N1 influenza pandemic does arise it is most likely to depend on whether or not viral strains involved in the present epidemic pick up more mutations that would enable efficient transfer of infection between humans. While there is no precedent in history for an H5N1 avian strain leading to widespread human-to-human transmission some form of influenza A pandemic is highly probable shortly.
The potential for an H5N1 influenza pandemic has underlined the numerous present limitations of treatment with antiviral drugs and vaccine manufacture and immunogenicity. Future vaccine approaches that could involve stronger induction of T-cell responses including cytotoxic T lymphocytes could offer greater protection than is currently provided by vaccines which are based on antibody neutralization of infection alone or predominantly.
Treatment of Influenza
Influenza has been a human threat throughout history, driven by the perpetual struggle between host immunity and evolutionary change in viruses. Strains are controlled through annual immunization and the repeated revaccination of the population, at great cost, complexity, and not invariably reliable, process. Vaccines are thus being developed to induce broadly cross-protective immunity to many influenza strains. Cross-immunity is widespread; in multistrain viral illnesses like influenza or dengue, recovery to initial infection can significantly modulate recovery to subsequent strain infection. Even distant viruses are able to be identified by identical cross-reactive T cells, Gostic et al. demonstrate that serious infection by a bird flu virus relies on the individual’s initial experience of influenza as a child.
Aspirin
Sore throat pain has been validated by European regulatory agencies as an appropriate pain model for acute, mild-moderate pain, and thus the findings of the sore throat pain clinical trials are generalizable to other types of acute pain. Likewise, the conclusions of a review of the effectiveness of a single dose of aspirin for the management of acute pain should also be generalizable to pain due to it. In this Cochrane review, the authors reviewed the outcome of 72 postoperative pain and acute trauma pain clinical trials and concluded that aspirin is an effective analgesic for moderate to severe intensity acute pain with an evident dose response.
Aspirin has been utilized for more than a century for the management of fever in URTI and, surprisingly, there are so few clinical trials regarding the efficacy of aspirin in the relief of fever in URTI. The initial studies on the impact of aspirin on fever did not include a placebo control and this renders the interpretation of the findings problematic.
It is only in recent times that a placebo-controlled trial has been done on the effectiveness of aspirin in the management of fever. Bachert et al. stated that single doses of 500 and 1000 mg aspirin were superior to placebo in lowering body temperature in patients with fever with URTI and also stated significant symptom relief of headache, achiness, and feverish discomfort.
Paracetamol
In spite of the availability of numerous new analgesics, paracetamol remains the most commonly employed analgesic antipyretic drug. Paracetamol is also the first line for most practitioners in the control of fever and relief of pain in a host of patients ranging from children and pregnant women, through the elderly and osteoarthritic subjects. There has been growing endorsement by practitioners to substitute ibuprofen for paracetamol as a first line for treatment of fever in children and infants.
Paracetamol relieves mild to moderate pain like headache toothache dysmenorrhoea and various postoperative pain in the dose range of 650 1300 mg in a broad range of controlled clinical trials.
Paracetamol is effective in relieving sore throat pain and fever of URTI in symptomatic relief. In a double blind placebo-controlled study in patients with sore throat pain due to URTI Schachtel et al. illustrated that a 650 mg single dose of paracetamol in 13 patients led to a significantly high decrease in subjective sore throat pain scores without any reported adverse effects.
In another double-blind placebo-controlled clinical trial on sore throat pain subjects with URTI Schachtel et al. showed that a single dose of 1000 mg paracetamol in 40 subjects induced a highly significant reduction of subjective sore throat pain scores with no side effects. In the second trial a 1000 mg paracetamol dose was demonstrated to be capable of subjective relief of sore throat pain up to 6.
Effectiveness in children
Paracetamol is particularly indicated for the relief of pain and fever in infants and children and it has a better safety profile than aspirin concerning Reyes syndrome. Standard recommended doses of paracetamol in the United Kingdom for infants and children. In a review of the first 40 years of paracetamol therapy in children the authors report paracetamol remains the first-choice OTC treatment for analgesia and antipyresis in children.
Safety for Influenza
In considering the safety of the analgesics for the treatment of symptoms of URTI it is necessary to understand that much of the concern over the use of nonsteroidal anti inflammatory drugs such as aspirin and ibuprofen is related to long term therapy with higher doses than available for OTC use for example in the treatment of rheumatoid arthritis. Similarly the safety of paracetamol has commonly been associated with alcohol intoxication and overdose.
Due to the sparse evidence from trials on the application of analgesics in URTI patients reliance on safety information collected from trials in other indications than URTI has to be made. These facts will not be addressed in detail since the reader can find the pertinent safety facts in in depth review articles and textbooks.
Only general issues regarding the safety of OTC analgesic doses for the management of URTI will be emphasized in this review. In one of the only reports to give data on the safety of aspirin paracetamol and ibuprofen when used in the management of symptoms of cold and flu the authors find that ‘ibuprofen used at OTC doses is as well tolerated as paracetamol and much better tolerated than aspirin.