Noval H1n12009 Swine-origin Influenza In Humans Historic Perspective

Novel 2009-H1N1 Swine-Origin Influenza in Humans: Historic Perspective. Dr. Kedar Karki 2007 report identified 37 civilian swine-origin influenza cases reported in the medical literature between 1958 and 2005. Of these cases, 19 occurred in the United States, six in Czechoslovakia, four in the Netherlands, three in Russia, three in Switzerland, one in Canada, and one in Hong Kong. Twenty-two (61%) reported recent exposure to pigs. The overall case fatality rate was 17%. Possible or probably limited human-to human transmission was reported in several situations. Between December 2005 and February 2009, 11 sporadic cases of infection in humans with triple-reassortant swine influenza A H1 viruses were reported to the Centers for Disease Control and Prevention. Ten of the infections were caused by triple reassortant H1N1 viruses and one by triple reassortant H1N2 virus. Seven cases involved either direct exposure to pigs or close proximity to pigs (ie, within 6 feet) shortly before illness onset. In two other cases the patients were in the general vicinity of pigs before illness onset, one was epidemiologically linked to a possible case, and one had no pig exposure. All patients survived the illness, although four were hospitalized and two required mechanical ventilation. Among the 10 patients with known clinical symptoms, nine reported fever, all had cough, six had a headache, and three reported diarrhea. An additional swine-origin influenza case occurred in Spain in 2008. An outbreak of swine-origin influenza was recognized in early 1976 among military personnel at Fort Dix, New Jersey. Thirteen clinical cases occurred with one death; the cause of the outbreak remains unknown, and no exposure to pigs was identified. Retrospective serologic testing subsequently demonstrated that up to 230 soldiers had been infected with the novel virus, which was an H1N1 strain. The outbreak did not spread beyond Fort Dix. Cases of novel H1N1 influenza were first identified in mid-April 2009 in California and soon thereafter in Texas and Mexico. The earliest recognized case occurred in Mexico with illness onset on March 17, 2009. Since that time, the virus has spread across the globe, and on June 11, 2009, the World Health Organization (WHO) declared the onset of an influenza pandemic. A recent analysis of global air traffic patterns illustrates how the virus spread via air travel from its likely source in Mexico to other areas of the world, most notably the United States. The numbers on August 14, 2009, were 7,511 hospitalizations and 477 deaths reported from 51 states and territories, including the 1

District of Columbia, American Somoa, Guam, Puerto Rico, and the US Virgin Islands. On July 16, 2009, the WHO ceased regular reporting of specific case counts, saying many countries were having difficulty tracking individual numbers and that their time would be better spent on investigating severe cases and other exceptional events. The cumulative total of cases reported from the various regional offices of WHO as of August 6, 2009, was 177,457, with 1,462 deaths, a number WHO acknowledges understates the actual numbers. In patients for whom clinical information was available, the most common presenting symptoms were fever (371 of 394 [94%]), cough (365 of 397 [92%]), and sore throat (242 of 367 [66%]). Diarrhea was present in 82 of 323 patients (25%) and vomiting in 74 of 295 patients (25%). Of the 399 patients for whom hospitalization status was known, 36 (9%) required hospitalization. Two patients died; one was a 23-month-old child and one was a pregnant 33-year-old woman. In a report from the WHO dated May 22, 2009, key clinical features of laboratory-confirmed cases for which data are available include the following. Most patients appear to have uncomplicated, typical influenza-like illness and recover spontaneously. The most commonly reported symptoms include cough, fever, sore throat, malaise, and headache. Fever has been absent in some patients. Almost one half of cases in the United States requiring hospitalization as well as 21 (46%) of 45 fatal cases in Mexico for which data are available involved underlying conditions, including pregnancy, asthma, other lung diseases, diabetes, morbid obesity, autoimmune disorders and associated immunosuppressive therapies, neurologic disorders, and cardiovascular disease. Among 20 pregnant women with H1N1 in the United States, three required hospitalization and one of these died. Among 45 fatal cases in Mexico, 54% of patients were previously healthy and most were 20 to 59 years of age. The median time from symptom onset to death was 10 days (range, 2 to 33 days). The clinical course for fatal cases in Mexico has been characterized by: Severe pneumonia with multifocal infiltrates (including nodular alveolar and, less frequently, basilar opacities) on chest x-ray (bacterial coinfections were documented in three fatal cases) Rapid progression to acute respiratory distress syndrome (ARDS) and renal or multiorgan failure (24% of fatal cases). Another study from Mexico found a significant increase in the rate of severe pneumonia between March 24 and April 29, 2009 (during the time of peak novel H1N1 influenza activity), with a shift in the age distribution to a younger segment of the population. The age-group 5 to 59 represented 87% of deaths from severe pneumonia compared to approximately 17% on average during other influenza epidemic periods. A case series of 18 patients with pneumonia caused by H1N1 influenza who were hospitalized in the Mexico City area during March 2

and April 2009 reported that 12 patients required mechanical ventilation and seven died most patients were previously healthy adults. These findings clearly demonstrate that novel H1N1 can cause severe disease and death in otherwise healthy persons. Scientists and public health officials have long been concerned that a reassorted influenza A virus could emerge in pigs and become a pandemic strain. Pigs can be infected with influenza A viruses from avian, human, or swine origin; therefore, pigs have been considered a "mixing vessel" for new viruses that can occur as a result of reassortment between viruses of diverse origins. Triple reassorted viruses containing genetic material from human, avian, and swine strains have been transmitted from pigs to humans and the current H1N1 strain appears to be a reassorted virus. Because this novel H1N1 virus is of swine origin, it is substantially different from human influenza A H1N1 viruses; therefore, a large proportion of the population might be susceptible to infection and the seasonal influenza vaccine H1N1 strain likely will not provide protection. These features enhance the pandemic potential of the new strain. Of interest, the 1918 pandemic began with a relatively mild "herald" wave in the spring of 1918. During that time, outbreaks were reported in Europe and in the United States particularly in military training camps for new recruits headed to the war in Europe. This first wave was followed by two additional waves in the fall and winter of 1918-19 that were much more severe. The second, highly virulent, wave spread rapidly around the world in the fall of 1918; it took only 2 months for the pandemic to circle the globe at that time. Of the three pandemics that occurred in the 1900s, two involved reassorted viruses, but none were reassortants with swine viruses. Recent genetic sequencing of the 1918 H1N1 strain indicates that the strain was of avian origin and that the strain did not reassort with a human strain, but rather gradually adapted to humans until it could be efficiently transmitted person to person. Current evidence indicates that the 1918 virus was an avian-like virus derived in toto from an unknown source. The 1957-58 pandemic, referred to as the "Asian flu," was caused by an H2N2 strain and originated in China. The pandemic strain acquired three genes from the avian influenza gene pool in wild ducks by genetic reassortment and obtained five other genes from the then-circulating human strain. The 1968-69 pandemic, referred to as the "Hong Kong flu," was caused by an H3N2 strain. The strain acquired two genes from the duck reservoir by reassortment and kept six genes from the virus circulating at the time in humans.The ill person should be kept away from others in the home as much as 3

possible (for example, in a separate bedroom with a separate bathroom). In addition, if possible, only one adult in the home should take care of the ill person (pregnant women should not care for ill persons). Caregivers who must have close contact with a person who has novel H1N1 infection should spend the least amount of time possible in close contact and try to wear a face mask for example, surgical mask or N-95 disposable respirator during close contact. If possible, consideration should be given to maintaining good ventilation in shared household areas. Persons in home isolation and their household members should be given infection control instructions, including practicing frequent hand washing with soap and water (or use alcohol-based hand gels containing at least 60% alcohol when soap and water are not available and hands are not visibly dirty). When the ill person is within 6 feet of others at home, the ill person should wear a face mask if one is available and the ill person is able to tolerate wearing it. Consideration should be given to providing antiviral medications (ie, oseltemivir [Tamiflu] or zanamivir [Relenza]) to prevent infection household contacts, particularly those contacts who may have chronic health conditions. The ill person should not have visitors other than caregivers. At this time, the Centers for Disease Control recommends that the primary means to reduce the spread of influenza in schools and childcare facilities are to focus on early identification of ill students and staff, to encourage students and school personnel to stay home when ill, and to stress good cough and hand hygiene etiquette. Decisions about school or childcare facility closure should be at the discretion of local authorities based on local considerations, including public concern and the impact of school absenteeism and staffing shortages. School closure is not advised for a suspected or confirmed case of novel influenza H1N1 and, in general, is not advised unless there is a magnitude of faculty or student absenteeism that interferes with the school's ability to function. Students, faculty, and staff with Influenza like Illness should stay home and not attend school or go into the community except to seek medical care for at least 7 days, even if symptoms resolve sooner. Students, faculty, and staff who are still ill 7 days after illness onset should continue to stay home from school until at least 24 hours after symptoms have resolved. Students, faculty, and staff who appear to have an Influenza like Illness at arrival or who become ill during the school day should be isolated promptly in a room separate from other students and then sent home. Parents and guardians should monitor their school-aged children, and faculty and staff should self-monitor every morning for symptoms of Influenza like Illness. Ill students should not attend alternative child care or congregate in settings other than school. School administrators should communicate 4

regularly with local public health officials to obtain guidance about reporting of Influenza like Illnesses in the school. Schools can help serve as a focus for educational activities aimed at promoting ways to reduce the spread of influenza, including hand hygiene and cough etiquette. Students, faculty, and staff should stringently follow sanitary measures to reduce the spread of influenza, including covering their nose and mouth with a tissue when coughing or sneezing (or coughing or sneezing into their sleeve if a tissue isn't available), frequently washing hands with soap and water, or using hand sanitizers. Use of face masks and respirators may help reduce the risk of acquiring influenza in crowded settings where there is potential for exposure to infectious persons. The Centers for Disease Control currently recommends that, whenever possible, rather than relying on the use of face masks or respirators, people should avoid close contact with people who might be ill and avoid being in crowded settings. However, the Centers for Disease Control also recommends that when close contact (ie, distances up to 6 feet) with others cannot be avoided, the use of face masks or respirators in areas where transmission of novel influenza A H1N1 virus has been confirmed should be considered as follows: Based on currently available information, for non-healthcare settings where frequent exposures to persons with novel influenza A H1N1 are unlikely, masks and respirators are not recommended. Persons who are ill with Influenza like Illness symptoms should stay home and limit contact with others as much as possible. When not alone or in a public place, people with Influenza like Illness should protect others by wearing face masks to reduce the number of droplets coughed or sneezed into the air and the time spent in crowded settings should be as short as possible. Respirators should be considered for use by individuals for whom close contact with an infectious person is unavoidable. This can include selected individuals who must care for a sick person (eg, family member with a respiratory infection) at home. Routine cleaning and disinfection strategies used during influenza seasons can be applied to the environmental management of swine influenza. Management of laundry, utensils and medical waste should also be performed in accordance with procedures followed for seasonal influenza. It is not anticipated that the seasonal influenza vaccine will provide protection against novel H1N1 infection. However, in some parts of the country, seasonal influenza viruses are still circulating. Influenza vaccination is effective against these seasonal viruses and

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should continue to be given to unvaccinated patients in areas where seasonal influenza cases are still occurring. According to the WHO, the Food and Animal Health Organization (FAO) of the United Nations, and the World Organization for Animal Health (OIE), influenza viruses are not known to be transmissible to people through eating processed pork or other food products derived from pigs. Heat treatments commonly used in cooking meat (eg, 70°C/160°F core temperature) will readily inactivate any viruses potentially present in raw meat products. Pork and pork products, handled in accordance with good hygienic practices recommended by the WHO, Codex Alimentarius Commission, and the OIE, will not be a source of infection. Authorities and consumers should ensure that meat from sick pigs or pigs found dead are not processed or used for human consumption under any circumstances.

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